PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


g 

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M  The    Chemical    Publishing    Co.  >j 

M  Easton,  Penna. 

•  Publishers  of  Scientific  Books 

g  Engineering  Chemistry  Portland  Cement 

**  Agricultural  Chemistry                     Qualitative  Analysis  g 

g  Household  Chemistry              Chemists'  Pocket  Manual  g 

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Principles  of  Agricultural  Chemistry 


BY 


G.  S.  FRAPS,  Ph.D. 

Associate  Professor  of  Agricultural  Chemistry,  Agricultural  and 

Mechanical  College  of  Texas.     Chemist,  Texas 

Experiment  Station.    State  Chemist 


E ASTON,  PA. 

THE  CHEMICAL  PUBLISHING  CO. 
1913 


LONDON,   ENGLAND 

WILLIAMS  &  NORGATE 

14  HENRIETTA  STREET,  COVENT  GARDEN,  W.  C. 


COPYRIGHT,  1913,  BY  EDWARD  HART. 


Preface. 


In  this  book  the  author  aims  to  present  the  fundamental  prin- 
ciples of  agricultural  chemistry.  The  point  of  view  is  that  of  the 
chemist  dealing  with  agricultural  problems;  the  attempt  is  made 
to  emphasize  chemical  methods  of  investigation,  and  inculcate 
scientific  habits  of  thought.  Details  are  omitted  so  far  as  they 
are  not  necessary  to  the  proper  treatment  of  the  subject.  Practi- 
cal applications,  which  are  necessarily  local,  are  left  out  as  much 
as  possible.  The  book  thus  treats  of  agricultural  chemistry 
rather  than  of  chemical  agriculture.  It  attempts  to  give  a  com- 
prehensive view  of  the  subject,  and  to  prepare  the  student  for  a 
more  detailed  study  of  its  various  phases. 

This  book  is  based  upon  lectures  given  for  a  number  of  years 
.to  students  in  Agriculture  at  the  Agricultural  and  Mechanical 
College  of  Texas.  A  number  of  references  are  given,  some  of 
which  do  not  refer  to  the  articles  in  which  the  facts  were  first 
published,  but  to  articles  of  interest  or  of  value  to  the  student, 
which  may  contain  numerous  references  to  the  literature  of  the 
subject.  It  was  not  deemed  desirable  nor  was  it  practical,  to 
give  references  for  all  the  statements  made  in  the  text. 

The  author  is  fully  aware  of  the  fact  that  there  is  room  for 
differences  of  opinion  as  to  what  should  be  treated  or  omitted  in 
a  work  of  this  character.  He  also  realizes  the  difficulty  of  avoid- 
ing errors,  arid  will  be  grateful  to  the  reader  who  may  bring 
errors  to  his  attention,  or  offer  suggestions  for  the  improvement 
of  the  book. 

Valuable  assistance  has  been  received  from  Mr.  S.  E.  Asbury, 
Assistant  State  Chemist,  and  especially  Dr.  C.  P.  Fountain, 
Professor  of  English. 

Agricultural  and  Mechanical 

College  of  Texas, 
Aug.  30,  1912.  College  Station. 


271665 


Contents. 


CHAPTER  PAGE 

I. — Introduction 7 

II.  — Essentials  of  Plant  Life 9 

III. — The  Plant  and  the  Atmosphere 35 

IV. -Origin  of  Soils 53 

V.  — Physical  Composition  and  Classes  of  Soils 79 

VI.— Physical  Properties  of  Soils 101 

VII.— The  Soil  and  Water  119 

VIII.— Chemical  Constituents  of  the  Soil 149 

IX.  —Chemical  Composition  of  the  Soil 167 

X.  — Active  Plant  Food  and  Water  Soluble  Constituents  of  the  Soil  180 

XI. — Chemical  Changes  in  the  Soil    204 

XII. — Soil  Deficiencies 244 

XIII.  —  Losses  and  Gains  by  the  Soil 271 

XI V.— Manure    280 

XV. — Sources  and  Composition  of  Fertilizers 293 

XVI.— Purchase  and  Use  of  Fertilizers 312 

XVII.— Constituents  of  Plants 346 

XVIII.— Composition  of  Plants 379 

XIX.  — Digestion 392 

XX.  -Utilization  of  Food 411 

XXL  — The  Maintenance  and  Fattening  Rations 435 

XXII.  — Feeding  Work  Animals  and  Growing  Animals 453 

XXIII. —Feeding  Milk  Cows 461 

XXIV. — Calculation  of  Rations 474 

Index   482 


Principles  of  Agricultural  Chemistry 


CHAPTER  I. 

INTRODUCTION. 

The  object  of  agriculture  is  the  profitable  production  of  useful 
plants  and  animals.  Agriculture  is  therefore  an  art  and  not  a 
science,  since  an  art  relates  to  something  to  be  done,  a  science 
to  something  to  be  known.  We  may,  however,  speak  of  the 
science  of  agriculture,  meaning  the  body  of  organized  knowledge 
appertaining  to  this  art. 

Success  in  agriculture  depends  upon  ability  to  manage  men  and 
things,  to  take  advantage  of  markets  and  local  conditions,  as  well 
as  upon  a  knowledge  of  how  to  produce  plants  and  animals,  and 
also  upon  skill  in  transforming  this  knowledge  into  practice. 
That  is  to  say,  practical  agriculture  is  a  business  and  business 
methods  must  be  followed  in  order  to  succeed  in  it. 

More  than  any  other  pursuit,  agriculture  is  underlaid  by  a  body 
of  complex  scientific  principles,  many  of  which  are  applied,  know- 
ingly or  unknowingly,  by  the  practical  farmer. 

Agricultural  Experiment  Stations. — The  importance  of  agricul- 
ture has  been  recognized  by  civilized  governments  in  the  establish- 
ment of  agricultural  experiment  stations  and  agricultural  colleges. 
The  oldest,  and  the  most  renowned  experiment  station,  that  at 
Rothamsted,  England,  is  not  a  State  institution,  but  was  estab- 
lished, conducted,  and  endowed  by  Sir  John  Lawes,  the  work 
having  been  begun  on  a  small  scale  in  1828.  Nearly  all  of  the 
experiment  stations  have  been  established  since  1870;  most  of 
those  in  this  country  date  from  1876  to  1882.  In  addition  to  con- 
ducting a  great  variety  of  experiments  along  agricultural  lines, 
these  stations  make  analyses  of  soils,  fertilizers,  feeding  stuffs, 
etc.  There  is  at  least  one  experiment  station  in  each  State  of  the 
United  States  and,  in  addition,  the  United  States  Department  of 
Agriculture  (U.  S.  D.  A.)  ;  these  agencies  are  doing  a  great  deal 
of  work  for  the  advancement  of  agriculture.  While  our  knowl- 


2  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

edge  of  the  principles  of  agriculture  is  largely  due  to  the  work  of 
the  experiment  stations,  it  is  chiefly  due,  let  it  be  said,  to  the  work 
of  chemists. 

Agricultural  Chemistry. — Agricultural  chemistry  is  the  applica- 
tion of  chemistry  and  chemical  methods  of  investigation  to 
agricultural  problems.  It  deals,  on  the  one  hand,  with  funda- 
mental causes  of  phenomena,  and,  on  the  other,  with  practical  ap- 
plications to  agricultural  practice.  The  chemist  was  the  first  of 
the  scientists  to  turn  his  attention  to  agriculture,  and  his  results 
were  so  fundamental,  and  practically  important,  and  the  science 
of  chemistry  was  capable  of  such  broad  application  to  agriculture, 
that  for  a  long  time  the  great  body  of  scientific  knowledge  re- 
garding agriculture  was  known  as  agricultural  chemistry. 
The  chemist  has  not  hesitated  to  avail  himself  of  the  sciences  of 
geology,  mineralogy,  physics,  botany,  or  such  other  sciences  as 
were  needed  in  the  solution  of  the  problems  at  hand.  Many  of  the 
problems  of  agriculture  are  complex,  and  their  solution  requires 
the  harmonious  cooperation  of  several  sciences.  Take,  for 
example,  the  transformation  of  organic  nitrogen  to  nitrates,  a 
very  important  process  in  the  soil.  This  is  a  chemical  change, 
accomplished  by  means  of  micro-organisms,  and  both  chemistry 
and  biology  are  necessary  to  give  a  complete  explanation  of  this 
phenomenon,  though  the  explanation  has  been  largely  worked  out 
by  the  chemist. 

Scope  of  the  Subject. — In  a  wide  sense,  agricultural  chemistry 
signifies  the  study  of  all  the  scientific  laws  involved  in  plant  and 
animal  growth,  whatever  the  several  sciences  which  may  be  in- 
volved. We  may  look  at  this  subject  as  a  fabric  in  which 
chemistry  is  so  interwoven  in  warp  and  woof  that,  if  removed, 
the  pattern  would  be  destroyed ;  if  the  other  sciences  were  re- 
moved, the  pattern  would  be  very  imperfect. 

It  shall  be  our  object  to  deal  with  the  principles  ascertained 
in  the  application  of  chemistry  to  agriculture,  taking  up  the  sub- 
ject from  the  view-point  of  the  chemist.  In  particular  we  shall 
attempt  to  indicate  the  methods  which  have  been  followed  in 
securing  important  results.  Agricultural  science  is  founded  upon 


INTRODUCTION  3 

and  grows  by  experiments.  An  experiment  is  a  question  put  to 
nature.  It  matters  not  what  theories  or  lack  of  theories  are  be- 
hind the  experiment,  if  the  question  is  carefully  and  skilfully 
put,  and  if  we  see  with  a  clear  eye,  not  dazed  by  prejudgment,  the 
answer  will  advance  our  knowledge.  The  knowledge  of  how  ex- 
periments have  been  planned  helps  us  to  plan  them  for  ourselves ; 
the  knowledge  of  how  a  certain  problem  has  been  solved  keeps  us 
from  regarding  the  knowledge  so  secured  as  dogmatic,  and  gives 
us  an  opportunity  to  test  it  for  ourselves  if  we  so  desire.  The 
scientific  investigator  cannot  accept  the  conclusions  of  others  at 
their  face  value;  he  must  examine  the  evidence  offered,  and 
satisfy  himself  that  the  evidence  justifies  the  conclusion. 

Division  of  the  Subject. — Agriculture  falls  naturally  into  two 
divisions — the  production  of  plants,  and  the  production  of 
animals.  Usually  in  the  case  of  plants,  only  a  portion  of  the 
plant  is  desired,  such  as  the  grain  ot  wheat  or  corn,  the  tubers 
of  potatoes,  etc.  The  remainder  is  considered  as  a  by-product 
and  such  disposition  is  made  of  it  as  appears  feasible.  The  dis- 
position of  the  by-product  has  considerable  effect  upon  the 
fertility  of  the  soil,  or  the  profits  of  agriculture.  In  some  cases, 
as  in  the  preparation  of  hay,  the  entire  plant  is  utilized.  In  other 
cases,  by-products  result  in  the  preparation  required  before  the 
product  can  be  placed  on  the  market,  such  as  threshing  of  wheat 
or  rice,  husking  or  shelling  of  corn,  etc. 

The  study  of  plant  production  involves  a  study  of  the  condi- 
tions which  are  favorable  to  plant  life,  the  composition  and  prop- 
erties of  the  atmosphere  and  the  soil,  the  maintenance  of  soil 
fertility,  fertilizers,  methods  of  soil  treatment,  etc.,  as  well  as 
the  composition  and  properties  of  the  plant  products,  and  a  study 
of  such  chemical  changes  as  are  involved  in  their  production  or 
preparation  for  market. 

The  study  of  animal  production  involves  a  study  of  the  prin- 
ciples of  animal  growth  and  nutrition,  the  composition  and  prop- 
erties of  feeding  stuffs,  their  preparation  or  preservation,  and  the 
methods  of  feeding  for  different  purposes,  such  as  meat,  milk, 
wool,  etc. 


4  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

We  will  begin  the  study  of  agricultural  chemistry  with  a  study 
of  the  chemical  laws  governing  the  production  of  plants.  We 
must  study  the  conditions  best  suited  to  the  growth  of  plants ; 
ascertain  how  these  conditions  are  filled  by  the  air  and  soil  in 
which  they  grow ;  learn  how  to  overcome  unfavorable  conditions 
in  the  soil,  and  how  to  maintain  and  increase  its  productiveness. 
In  addition,  we  must  study  the  composition  of  the  plant. 

Agriculture    Primarily  the   Production   of  Organic  Matter.— 

Agriculture  deals  primarily  with  the  production  of  organic  mat- 
ter. Organic  matter,  for  the  purpose  of  the  agriculturalist,  may 
be  defined  as  the  compounds  of  carbon  which  possess  chemical 
energy.  In  agriculture,  inorganic  compounds  of  carbon  and  other 
bodies  are  caused  to  combine  with  the  energy  of  the  sun,  so  as  to 
produce  organic  compounds  containing  energy,  which  may  supply 
heat  or  energy  for  the  use  of  man  or  other  animals,  which  may 
serve  as  fuel,  or  be  used  for  other  purposes.  The  primary  object 
of  agriculture  is  thus  to  store  up  the  energy  of  the  sun.  The 
production  of  organic  matter  is  accomplished  by  means  of  plants. 

Products  of  Plant  Life. — The  various  soil  and  atmospheric 
agencies,  acting  upon  the  life  within  the  seed,  produce  a  plant 
built  up  by  sunshine,  water,  carbon  dioxide  from  the  air,  and  sev- 
eral mineral  substances  from  the  earth.  The  plant  is  composed 
mostly  of  complex  organic  substances,  rich  in  carbon,  and  con- 
tains a  comparatively  small  amount  of  material  withdrawn  from 
the  soil.  It  is  suitable  for  the  food  of  animals,  while  the  ma- 
terials from  which  it  is  built  are  not.  If  dried  and  heated 
sufficiently,  the  plant  burns  and  gives  off  heat. 

It  has  been  found  that  the  heat  which  is  secured  in  the  burning 
of  plants,  or  which  can  be  utilized  as  heat  or  other  forms  of 
energy  by  animals  which  consume  them,  comes  from  the  sun.  The 
energy  of  the  sun  is  used  to  decompose  carbon  dioxide,  water, 
and  nitrates,  and  to  form  complex  organic  compounds.  These 
bodies  then  contain  stores  of  energy  which  can  be  utilized  by 
animals  or  in  other  ways.  Plants  thus  store  up  the  energy  of  the 
sun,  and  may  also  be  regarded  as  media  for  furnishing  animals 


INTRODUCTION  5 

with  the  sun's  energy.  All  energy  utilized  by  plants  or  animals 
thus  comes  directly  or  indirectly  from  the  sun. 

We  have  used  the  term  ''organic"  in  connection  with  the  com- 
pounds formed  in  plants.  It  was  believed  in  the  beginning  of  the 
1 9th  century  that  organic  bodies,  such  as  starch,  sugar,  urea,  etc., 
differed  greatly  in  chemical  nature  from  inorganic  bodies,  and 
could  only  be  formed  under  the  influence  of  mysterious  life- 
forces.  But  in  1820  Wohler  prepared  a  product  of  animal  life 
found  in  the  urine,  called  urea,  from  a  purely  inorganic  body,  am- 
monium cyanate.  The  supposed  barrier  between  organic  and  in- 
organic substances  was  thus  broken  down;  great  numbers  of 
organic  compounds  have  since,  been  prepared,  some  of  which 
occur  in  nature,  and  the  chemist  now  hardly  places  bounds  to  the 
possibilities  of  organic  synthesis  in  the  laboratory.  It  is  well 
known  that  organic  and  inorganic  bodies  obey  the  same  laws, 
though  on  account  of  the  size  and  complexity  of  the  subject, 
organic  chemistry  is  still  treated  separately. 

As  far  as  agricultural  chemistry  is  concerned,  there  is  a  wide 
difference  between  organic  and  inorganic  bodies.  Organic  com- 
pounds may  serve  as  food  for  animals,  but  inorganic  do  not.  On 
the  other  hand,  inorganic  bodies  serve  as  food  for  plants ;  but  to 
only  a  very  limited  extent,  if  at  all,  do  plants  make  use  of  organic 
bodies.  With  the  aid  of  light,  plants  build  up  organic  bodies 
which  possess  chemical  energy,  from  inorganic  bodies  which  do 
not  possess  chemical  energy.  For  the  student  of  agriculture, 
organic  compounds  are  compounds  of  carbon  which  possess 
chemical  energy,  and  they  are  usually  the  products  of  plants  or 
animals. 

Conditions  of  Plant  Life. — The  conditions  necessary  for  the 
production  of  organic  matter  by  green  plants  may  be  summed  up 
briefly  as  follows: 

(1)  Light. 

(2)  Favorable  Temperature. 
'  (3)   Water. 

(4)   Certain  elements  in  certain  forms  of  combination. 
If  any  of  these  conditions  are  unfavorafre,  the  plant  will  suffer 


0  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

and  perhaps  die.  The  varying  needs  of  different  kinds  of  plants 
and  their  varying  powers  of  satisfying  these  needs,  permit  plants 
to  flourish  in  nature  under  a  great  diversity  of  conditions,  as  in 
the  tropics,  or  in  arctic  regions,  in  shade  or  in  sunshine,  in  water 
or  in  deserts.  The  conditions  of  temperature,  light,  or  water 
favorable  to  cultivated  plants  are  more  limited  than  those  of  wild 
plants,  but  still  the  range  is  wide. 

The  simple  conditions  we  have  named  are  rendered  more  com- 
plex by  the  varying  degree  in  which  different  classes  of  plants 
require  them,  and  the  varying  powers  they  have  of  supplying  their 
needs.  The  varying  powers  of  soils  to  supply  the  needs  of  the 
plant  growth  thereon,  and  the  necessity  of  maintaining  the 
fertility  of  the  soil,  render  the  matter  still  more  complex. 

Relation  of  the  Plant  to  the  Atmosphere. — The  atmosphere  has 
its  part  in  supplying  some  of  the  conditions  for  the  growth  of 
plants,  the  more  important  being  light,  heat,  carbon  dioxide,  and, 
indirectly,  water.  The  atmospheric  conditions  are  less  susceptible 
to  control  than  soil  conditions;  nevertheless,  sometimes  a  partial 
control  is  established,  as  temperature  and  humidity  in  green 
houses,  light  in  the  growth  of  plants  by  artificial  light  or  under 
shade,  and  the  prevention  of  frost  by  smoke  clouds.  The 
atmosphere  indirectly  supplies  the  plant  with  small  quantities  of 
combined  nitrogen,  through  the  soil. 

Relation  of  the  Plant  to  the  Soil. — The  relation  of  the  plant  to 
the  soil  is  more  complex  than  its  relation  to  the  atmosphere. 
The  functions  of  the  soil  are  primarily  to  support  the  plant,  sup- 
ply it  with  water  and  certain  necessary  elements,  and  maintain  a 
favorable  temperature.  These  are,  however,  fulfilled  in  a  very 
complicated  manner. 

Methods  of  Experiment. — The  methods  of  studying  the  problems 
of  agricultural  chemistry  must  be  varied  to  suit  the  end  in  view. 
At  various  points  we  shall  bring  in  experimental  evidence  in  sup- 
port of  certain  views,  thus  illustrating  by  example  some  of  the 
more  important  methods.  The  earnest  student  is  advised  to  study 


INTRODUCTION  7 

the  original  papers  that  mark  important  steps  in  agricultural 
science. 

The  problems  of  agricultural  chemistry  are  often  so  complex 
and  interrelated  as  to  render  their  solution  very  difficult.  In  the 
study  of  them,  one  should  endeavor  to  vary  one  factor  at  a  time 
and  keep  the  others  constant.  Let  us  take,  for  example,  the  es- 
sential elements  in  plants.  By  chemical  analysis  we  can  ascertain 
that  plants  contain  certain  elements.  Which  of  these  are 
necessary  to  the  plant  and  which  are  not?  The  solution  of  the 
problem  is  obtained  by  growing  the  plants  under  the  most  favor- 
able conditions,  with  an  ample  supply  of  all  the  elements  found  in 
the  plant  except  one.  If  the  plant  does  well,  then  this  one  is  not 
needed.  If  it  does  very  poorly,  and  all  the  conditions  are  most 
favorable,  then  the  element  is  necessary.  The  difficulties  in  fol- 
lowing out  this  method  of  experiment  will  be  presented  later. 

It  is  obvious  that  if  two  variables  are  present,  it  would  be  im- 
possible to  tell  which  one  produced  a  given  effect,  or  what  part 
each  had  in  it.  The  conditions  of  agricultural  experimentation 
are  sometimes  such  that  it  is  difficult  to  reduce  the  experiment  to 
a  variation  in  one  variable,  and  sometimes  proper  precautions  are 
not  taken  to  eliminate  other  variables.  Take,  for  example,  a  field 
experiment  on  corn,  or  any  other  crop.  Variables  are  weather, 
insects,  seed,  soil,  etc.  We  attempt  to  eliminate  them  by  sub- 
jecting the  entire  field  to  the  same  conditions,  but  it  is  very 
difficult  to  make  all  conditions  uniform. 

Agricultural  investigations  must  be  brought  to  the  test  of  ac- 
tual conditions.  Conditions  in  the  laboratory  or  in  pot  experi- 
ments, are  often  radically  different  from  those  which  prevail 
in  practice.  The  gap  between  the  two  must  be  bridged  by  ex- 
periment, rather  than  by  theory. 

Observation  and  Experience. — Agricultural  knowledge  is 
largely  based  upon  observation  and  experience.  General  agricul- 
tural practice  is  based  upon  experience,  passed  on  from  one 
generation  to  another.  Experience  is,  indeed,  based  upon  ex- 
periments, though  the  experiments  are  not  always  consciously 


8  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

made,  \ery  often  imperfectly  planned  and  often  very  expensive. 
Sometimes  the  trial  is  made  intentionally,  and  sometimes  the 
trials  are  more  or  less  unintentional  and  due  to  ignorance. 
Usually  the  trials  are  very  limited  in  scope,  and  therefore  differ 
widely  from  consciously  organized  experiments  dealing  with  de- 
finite problems. 


CHAPTER  II. 


ESSENTIALS  OF  PLANT  LIFE. 

Prior  to  1840,  comparatively  little  was  done  to  apply  chemistry 
to  the  solution  of  agricultural  problems.  Much  information  was 
collected  regarding  the  chemical  composition  of  soils,  plants,  and 
animals,  and  a  few  books  discussing  the  i  elation  of  chemistry  to 
agriculture  were  published,  those  of  Sir  Humphrey  Davy  and 
Thaer  being  perhaps  the  most  important,  but  the  fundamental 
principles  of  plant  and  animal  nutrition  were  not  recognized,  and 
the  books  offered  little  of  practical  importance  to  the  farmer. 

At  that  time  the  prevailing  theory  was  that  plants  feed  upon 
the  organic  matter,  or  humus,  of  the  soil,  just  as  animals  feed  on 
organic  matter.  According  to  this  theory,  the  soil  should  be  kept 
full  of  vegetable  matter  to  feed  the  plant.  The  ash  or  mineral 
matter  of  the  plant,  whose  presence  was  known  and  could  not  be 
ignored,  was  thought  to  act  as  a  stimulant,  and  not  as  food.  In- 
deed, Thaer,  and  perhaps  others,  held  that  mineral  matter  could 
be  created  by  plants. 

The  great  German  chemist,  Justus  von  Liebig,  in  1840  publish- 
ed a  little  book  entitled  "Chemistry  in  its  Application  to  Agricul- 
ture and  Physiology,"  which  developed  an  entirely  new  theory  of 
plant  nutrition.  Plants,  he  said,  do  not  secure  their  organic  mat- 
ter from  the  soil,  but  from  the  air.  He  showed  by  calculations 
that  there  is  not  enough  organic  matter  in  the  soil  to  produce 
average  yields  of  farm  crops.  The  material  of  importance  which 
comes  from  the  soil,  he  said,  is  the  mineral  matter.  Supply  the 
soil  with  a  sufficiency  of  mineral  matter,  and  it  will  remain  fertile, 
regardless  of  its  content  of  organic  matter.  Such,  in  brief,  was 
Liebig's  mineral  theory  of  plant  nutrition.  This  was  a  practical 
theory  and  easily  tested.  Liebig  himself,  as  an  object  lesson, 
transformed  a  barren,  sandy  piece  of  land  near  Giessen,  Germany, 
into  a  beautiful  garden,  by  means  of  his  mineral  manures.  Mr. 
John  Lawes  was  incited  to  begin  field  experiments  at  his  manor 
of  Rothamsted,  England. 

These  experiments  led  to  the  discovery  of  the  process  of  mak- 


IO  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

ing  acid  phosphate  by  treating  phosphate  rock  with  sulphuric 
acid.  The  process,  which  was  patented,  became  the  foundation 
of  the  fertilizer  industry.  The  Rothamsted  experiments,  prob- 
ably the  most  famous  field  experiments  yet  instituted,  have  been 
carried  on  with  the  same  applications  of  fertilizers  and  manure 
since  1852.  Sir  John  Lawes  endowed  the  Rothamsted  Ex- 
periment Station,  and  made  provision  for  continuing  its  work 
indefinitely.  The  great  fertilizer  industries,  and  the  era  of 
agricultural  experimentation,  may  be  said  to  date  from  the  ap- 
plication of  chemistry  to  agriculture  made  by  von  Liebig  in  1840. 

Evidence  for  the  Mineral  Theory. — As  evidence  that  the  organic 
matter  of  the  soil  is  not  necessary  to  plants,  plants  have  been 
grown  to  full  maturity  in  soils  from  which  all  the  organic  mat- 
ter had  been  burned  out.  Plants  were  also  grown  in  pure  water 
containing  no  organic  matter,  or  carbon,  to  which  certain  mineral 
salts  had  been  added.  A  prize  was  offered  by  the  University  of 
Gottingen  for  the  solution  of  the  question,  whether  the  ash  of 
plants  was  taken  from  the  soil  or  created  by  them.  Such  prizes 
are  still  offered  in  Europe.  This  prize  was  won  by  Weigmann 
and  Polstorff.1  In  their  first  series  of  experiments,  they  grew  a 
number  of  plants  of  different  kinds,  upon  sand  from  which  the 
soluble  materials  had  been  removed,  as  far  as  possible,  by  extrac- 
tion with  strong  acids.  One  set  of  plants  received  only  distilled 
water,  the  other  set  received  a  mixture  of  the  mineral  salts  found  in 
the  ash  of  plants,  and  nitrates.  The  plants  which  received  distilled 
water  hardly  grew  at  all,  but  the  others  grew  well.  This  was 
evidence  that  the  mineral  matter  was  necessary  for  the  growth 
of  the  plants.  The  plants  grown  on  the  sand  with  distilled  water 
alone,  when  burned,  were  found  to  contain  slightly  more  ash  than 
was  present  in  the  same  quantity  of  seed  from  which  they  were 
grown.  Weigmann  and  Polstorff  thought  that  this  gain  came 
from  the  sand.  They  accordingly  instituted  further  experi- 
ments and  grew  plants  in  a  platinum  dish  on  platinum  scraps 
with  distilled  water,  the  seed  being  weighed.  Upon  incineration, 
the  quantity  of  ash  in  the  plants  was  found  to  be  exactly  equal  to 
1  Dissertation,  1842,  cited  Meyer's  Agricultur  Chemie. 


ESSENTIALS  OF  PLANT  U?E  II 

the  quantity  of  ash  in  the  seed  planted.  Hence  the  plants  did  not 
create  any  ash,  and  the  ash  gained  in  the  previous  experiment 
must  have  come  from  the  sand.  This  work  is  an  example  of  the 
importance  of  continuing  experiments  until  only  one  possible 
conclusion  is  indicated,  and  also  shows  the  danger  of  formulating 
conclusions  upon  insufficient  data. 

The  plants  in  the  platinum  dish  after  reaching  the  height  of 
only  two  or  three  inches,  began  to  turn  yellow,  and  died.  This 
showed  that  the  ash  in  the  seed  was  sufficient  for  only  a  limited 
development  of  the  plant,  and,  taken  in  connection  with  the  pre- 
ceding experiment,  showed  the  mineral  matter  was  necessary 
to  the  growth  of  plants. 

Finding  the  Essential  Elements. — An  essential  element  is  an 
element  whose  presence  is  absolutely  necessary  to  the  full  growth 
and  maturity  of  the  plant.  A  useful  element,  though  not  essential, 
may  be  serviceable  to  the  plant. 

The  following  fourteen  elements  are  invariably  present  in 
plants : — 

The  eight  non-metals:  carbon,  hydrogen,  oxygen,  nitrogen, 
phosphorus,  sulphur,  silicion  and  chlorine. 

The  six  metals:  potassium,  calcium,  magnesium,  iron,  sodium 
and  manganese. 

Other  elements  are  sometimes  found  in  plants.1  Iodine  occurs 
constantly  in  sea-weeds  and  sponges,  being  present  as  an  organic 
compound  in  the  latter.  It  is  prepared  from  the  ash  of  sea-weeds. 
Fluorine,  arsenic,  boron,  rubidium,  bromine,  lithium,  barium, 
aluminum,  thallium,  lead,  zinc,  titanium  and  copper  have  also 

Water  Culture  Experiments. — Experiments  to  ascertain  which 
been  found  in  plants,  in  minute  quantities. 

elements  are  essential  or  useful  to  plants  are  made  by  growing 
plants  in  pure  water,  to  which  the  salts  to  be  tested  are  added. 
This  is  known  as  the  water  culture  method,  and  is  used  because  it 
is  comparatively  easy  to  secure  pure  water  and  salts,  but  almost 
impossible  to  secure  a  sand  or  soil  from  which  plants  do  not  ex- 

1  Jahresber.  Agr.  Chem.,    1864,  pp.  94,  99,  159;  1866,  p.  121.     Exp.  Sta. 
Record  3,  p.  717;  7,  p.  643. 


12  PRINCIPLES  OF  AGRICULTURAL,  CHEMISTRY 

tract  some  substance.  Only  the  fourteen  elements  invariably 
found  in  plants  need  be  considered,  and  as  two  of  these  (hydrogen 
and  oxygen)  are  in  the  water,  and  one  (carbon)  is  supplied  from 
the  air,  there  remains  eleven  to  be  tested.  Twelve  solutions  are 
prepared.  One  contains  all  eleven  elements,  and  is  used  as  a 
check.  If  the  plant  does  not  thrive  in  it,  something  is  wrong 
with  the  experiment.  Each  of  the  other  solutions  contain  salts 
of  ten  elements,  one  being  left  out  of  each  solution.  For  ex- 


Fig.  i.— Buckwheat  grown  in  complete  nutrient  solution  (O) 
and  with  Cl,  K,  etc.,  absent. 

ample,  sodium  is  left  out  of  one,  potassium  left  out  of  another, 
and  so  on.  Seeds  are  germinated  on  moist  filter  paper,  and  the 
strongest  seedlings  are  supported  by  a  cleft  cork  in  the  neck  of  the 
bottle  containing  the  nutrient  solution,  so  that  the  roots  are  im- 
mersed, but  the  cotyledons  are  above  the  surface.  The  plants 
would  probably  die  if  the  cotyledons  were  immersed.  The  vessel 


ESSENTIALS  OF  PLANT  UFE  13 

is  covered  with  black  paper  to  exclude  light  and  so  prevent  the 
growth  of  green  algae,  which  interfere  with  the  success  of  the 
experiment.  The  nutrient  solution  is  replaced  by  a  fresh  solu- 
tion every  few  days,  to  avoid  injury  to  the  plants  by  change  in 
the  chemical  composition  of  the  solution.  Absorption  of  excess 
of  acid  or  basic  radicals  by  the  plants,  leaves  the  liquid  acid  or 
alkaline,  according  to  its  previous  composition. 

Where  the  plant  grows  well,  reaches  a  good  size,  and  produces 
seed,  the  element  absent  from  the  solution  is  not  essential. 
Where  the  plant  makes  a  very  poor  and  imperfect  growth,  and 
produces  only  a  few  seed,  or  none  at  all,  the  element  absent  from 
the  solution  is  essential.  Since  the  seed  always  contain  a  certain 
quantity  of  the  essential  elements,  some  growth  of  the  plant  is  to 
be  expected. 

The  results  of  one  series  of  experiments,  are  not,  of  course,  con- 
sidered final.  In  experimental  work,  the  work  of  one  man  has 
usually  to  be  confirmed  by  that  of  others,  before  it  receives  gen- 
eral acceptance. 

The  method  of  experiment  known  as  "water  culture"1,  is 
suitable  for  experiments  in  which  the  material  supplied  to  the 
roots  must  be  accurately  controlled.  It  is  impossible  to  secure  a 
soil  or  a  sand  from  which  plants  will  not  obtain  some  mineral 
material.  Weigmann  and  Polstorff,  as  we  have  seen,  found  that 
plants  extracted  ash  from  sand  which  had  been  exhausted  with 
strong  acids,  and  other  workers  have  had  similar  experiences.  By 
using  pure  water  and  pure  salts,  we  know  exactly  what  material 
is  presented  to  the  roots  of  the  plants.  The  plant  may  take  up  a 
small  portion  of  the  silica  from  the  glass  when  the  experiment  is 
conducted  in  glass  vessels,  but  this  is  not  usually  of  importance. 
If  necessary,  vessels  of  platinum  or  of  paraffin,  can  be  used. 

The  Essential  Elements. — It  has  been  found  by  experiments 
such  as  those  described  above,  that  the  following  elements  are, 
without  doubt,  essential  to  the  life  and  growth  of  plants : 

The  four  metals :  potassium,  calcium,  magnesium,  and  iron. 

The  three  non-metals :  nitrogen,  sulphur,  and  phosphorus. 
1  Knop,  Sachs  and  others,  Jahresber.  Agr.  Chem.,  1861,  pp.  126,  136. 


14  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  non-metals:  carbon,  hydrogen  and  oxygen,  secured  from 
the  air  and  water,  as  already  stated,  are  essential.  A  soil,  to  be 
fertile,  must  supply  to  the  plant  an  abundance  of  potassium, 
calcium,  magnesium,  iron,  nitrogen,  sulphur,  and  phosphorus. 

Plants  can  be  grown  to  full  maturity  by  means  of  the  follow- 
ing solution: — 

One  gram  calcium  nitrate, 

0.25  gram  potassium  nitrate, 

0.25  gram  potassium  sulphate, 

0.25  gram  magnesium  sulphate, 

0.20  gram  ferrous  phosphate. 

1,000  cc  distilled  water. 

Chlorine  Essential  but  Unimportant. — Experiments  to  ascertain 
whether  or  not  chlorine  is  essential  to  plants  were  at  first  con- 
flicting. Three  independent  investigators  grew  plants  in  water 
culture  to  full  and  complete  maturity  without  chlorine.  Knop 
grew  corn,  buckwheat  and  cress ;  Wagner  grew  corn ;  and  Birner 
grew  oats. 

On  the  other  hand,  Nobbe  and  Siegert1  found  that,  although 
buckwheat  grew-  well  in  water  culture  without  chlorine  up  to  the 
time  of  flowering,  a  little  later  the  tips  of  the  stalks  died  off,  the 
leaves  became  brittle,  spotted,  and  fluffy,  starch  accumulated  in 
the  stems  and  no  seed  were  produced.  The  diseased  condition 
was  remedied  by  the  addition  of  chlorine.  Chlorine  thus  appear- 
ed to  be  essential  to  the  formation  of  the  seed  of  buckwheat. 
Leydhecker2  also  found  that  buckwheat  would  not  seed  in  absence 
of  chlorine,  and  Nobbe  later  confirmed  previous  results  by  a  sec- 
ond series  of  experiments. 

Thus  one  group  of  investigators  finds  chlorine  not  essential,  the 
other  group  finds  that  it  is  essential.  These  contradictory  results 
are  explained  by  the  work  of  Bayer.3  Bayer  grew  oats  in  water 
culture,  with  and  without  chlorine,  all  the  other  essential  elements 
being,  of  course,  present.  With  chlorine  12.5  grams  seed  were 

1  Landw,  Vrersuchs-stat. ,  1863,  p.  116;  1865,  p.  377. 

2  Ibid,  1866,  p.  177. 

3  Landw.  Versuchs-stat.,  7,  p.  370. 


ESSENTIALS  OF  PLANT 

secured,  without  chlorine  7.5  grams  of  seed.  Apparently  chlorine 
was  not  essential.  The  seed  grown  in  the  absence  of  chlorine 
were  found,  on  analysis,  to  be  nearly  free  from  chlorine.  These 
seeds  were  used  in  another  experiment  in  water  culture  as  before, 
with  and  without  chlorine.  With  chlorine,  they  made  seed ;  with- 
out chlorine,  they  failed  to  produce  seed.  Chlorine,  therefore, 
is  essential.  The  seed  used  in  the  first  series  of  experiments  con- 


Fig.  2. — Pot  experiment  showing  soil  deficient  in  nitrogen 
and  in  phosphoric  acid.     Texas  Station. 

tained  a  sufficient  quantity  of  chlorine  for  the  full  development 
of  the  plant,  but  those  used  in  the  second  experiment  did  not. 

There  are  a  number  of  instances  in  which  apparently  con- 
tradictory results  of  different  workers  have  been  reconciled  by 
further  investigation. 

The  opposite  results  of  the  investigators  referred  to  above  are 
due,  in  one  case,  to  the  presence  of  sufficient  chlorine  in  the  seed 
used;  in  the  other  case,  to  insufficient  chlorine  in  the  seed.  We 
may  conclude  that  chlorine  is  essential  to  the  plant,  but  the  min- 
ute quantity  required  may  be  present  in  the  seed.  Chlorine  is 


1 6  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

needed  in  such  small  quantity  that  it  need  hardly  be  considered  as 
a  plant  food  by  the  agricultural  chemist. 

Silicia  not  Essential  but  Useful. — Silica  is  present  in  all  plants 
grown  under  normal  conditions,  and  makes  up-  a  considerable 
proportion  of  the  ash  of  some  plants.  The  ash  of  cereal  straws 
contain  20  to  40  per  cent.  It  was  formerly  thought  that  silica 
was  essential  to  the  strength  of  cereal  straws.  Plants  have  been 
grown  to  maturity  without  silica,  though  they  secured  traces  from 
the  glass  vessels  in  which  the  solutions  were  contained.1  The 
plants  attained  a  normal  development,  and  produced  seed  well. 
Silica  is,  therefore,  not  essential  to  plant  life.  Though  not 
essential,  silica  is  useful.  In  certain  water  culture  experiments 
by  Kreuzhaga  and  Wolff2  with  oats,  the  presence  of  the  silica 
increased  both  the  number  and  the  weight  of  the  seed.  The 
silica  appeared  to  aid  the  plant  to  mature  and  form  seed.  The 
following  table  shows  the  results  of  an  experiment  in  which  all 
conditions  were  constant  except  the  silica: — 


• 

Number  of 
seed 

Weight  of  seed 
in  grams 

71  e 

2T. 

T  ittle  silica 

1>uoV 

*•* 

46 

The  silica  is  supposed  to  cause  the  leaves  to  die  off  during  the 
ripening  of  the  fruit,  allowing  essential  elements  to  be  withdrawn 
and  utilized  in  formation  of  seed.  According  to  Wolff,  if  silica 
is  absent  from  the  solution,  oats  will  produce  empty  seed  heads 
unless  an  excess  of  phosphoric  acid  is  present.  The  silica  thus 
economizes  phosphoric  acid,  and  this  is  a  highly  useful  function. 
Hall  and  Morison,3  at  the  Rothamsted  Station,  show  that  silica 
used  as  a  fertilizer  causes  an  increased  yield  and  earlier  forma- 
tion of  the  grain  of  barley,  but  causes  the  plant  to  take  up  more 
phosphoric  acid  from  the  soil. 

Soda  Not  Essential. — Soda  is  never  absent  entirely  from  any 

1  Sachs,  Jahresber.  Agr.  Chem.,  1862,  p.  97. 

2  Landw.  Versuchs-stat.,  1884,  P-  T6i. 

3  Proc.  Roy.  Soc.,  1906,  p.  445. 


ESSENTIALS  OF  PLANT  UFE  I/ 

plant.  It  has  been  impossible  to  exclude  soda  completely  in  water 
culture  experiments,  owing  to  its  presence  as  impurities  in 
reagents,  and  its  entrance  into  solution  by  the  action  of  water 
upon  glass  vessels,  but  otherwise  such  experiments  show  that 
soda  is  not  essential.  Soda  does  not  appear  to  perform  any  such 
highly  useful  functions  as  silica.  It  may,  however,  take  the  place 
of  the  indifferent  essential  ash,  and  so  replace  potash. 

Definition  of  Plant  Food. — Plant  food  may  be  defined  as  any 
substance  which  contributes  to  the  building  of  tissue  or  is  other- 
wise essential  to  the  life  of  plants.  Carbon  dioxide,  which  is 
assimilated  by  the  leaves,  is  plant  food,  and  so  is  water.  But  we 
are  more  concerned  in  agriculture  with  the  mineral  salts  which 
enter  the  roots  of  plants,  since  these  require  control  and  are  more 
or  less  subject  to  it,  and  we  have  these  in  mind  rather  than  car- 
bon dioxide  or  water  when  we  speak  of  plant  food.  By  plant 
food  we  usually  mean  potash,  phosphoric  acid,  nitrogen,  sul- 
phates, lime,  magnesia,  or  iron.  Often  the  term  is  confined  to 
nitrogen,  phosphoric  acid,  and  potash,  for  the  reason  that  they 
are  the  only  forms  of  plant  food  commonly  added  to  the  soil. 

\Ye  have  spoken  of  the  elements  essential  to  plants,  but  we  must 
bear  in  mind  that  the  free  elements,  with  two  exceptions,  are  use- 
less to  plants.  These  two  exceptions  are  oxygen,  which  is  given 
off  by  plants  to  a  much  greater  extent  that  it  is  used,  and  nitrogen, 
which  in  the  free  state  can  be  taken  up  by  leguminous  plants,  if 
the  bacteria  which  aid  in  this  process  are  present.  All  the  other 
elements  in  the  free  state  are  either  useless  or  injurious  to  plants. 
The  essential  elements  must  be  present  in  certain  forms  of  com- 
bination ;  other  combinations  are  injurious  or  useless.  These 
facts  have  been  ascertained  by  numerous  experiments  with  water 
cultures  and  sand  cultures. 

Iron  is  taken  up  as  ferric  compounds;  ferrous  compounds  are 
often  injurious.  Phosphorus  must  be  present  as  phosphates,  sul- 
phur as  sulphates,  chlorine  as  chlorides,  silica  as  silicates  or  silicic 
acid.  Sulphides,  sulphites,  chlorates,  and  perchlorates,  are 
injurious  to  plants.  Carbon  is  absorbed  as  carbon  dioxide, 
and  as  organic  bodies  to  a  much  less  extent.  Oxygen 


i8 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


is  taken  up  in  water,  in  carbon  dioxide,  and  as  free 
oxygen.  Nitrogen  enters  the  plant  in  nitrates,  ammonia,  as  free 
nitrogen,  and  to  some  slight  extent  in  organic  bodies.  Hydrogen  is 
taken  up  as  water  and  ammonia.  Since  these  elements  are  pres- 
ent in  the  soil  in  the  oxidized  condition,  and  are  taken  up  by 
plants  in  that  form,  and  not  as  elements,  plant  food  is  usually 
referred  to  and  estimated  in  the  form  of  the  oxides.  We  speak 
of  phosphoric  acid  (P^Og),  potash  (K2O),  soda  (Na2O),  lime 
(CaO),  magnesia  (MgO),  oxide  of  iron  (Fe2O3)  and  silica 
(SiO2).  These  terms  are  used  almost  exclusively  in  agriculture 
and  especially  in  the  analysis  of  soils  and  fertilizers.  We  speak 
of  nitrogen  (N)  and  chlorine  (Cl),  for  the  former  may  or  may 
not  be  present  in  the  oxidized  condition,  and  the  latter  is  injur- 
ious when  oxidized. 

Quantity  of  Plant  Food  Required. — The  method  of  determining 
the  exact  quantity  of  plant  food  required  is  tedious  and  difficult 
and  has  been  applied  only  to  two  or  three  plants. 

To  determine  the  minimum  quantity  of  phosphoric  acid  re- 
quired by  oats,  WViff1  grew  eight  sets  of  six  oat  plants  each  in 
water  cultures.  One  solution  contained  an  excess  of  all  the 
essential  forms  of  plant  food,  except  phosphoric  acid.  The  other 
solutions  received  increasing  amounts  of  phosphoric  acid.  All 
conditions  were  the  same,  excepting  the  varying  amounts  of  phos- 
phoric acid.  When  the  oats  were  ripe,  they  were  harvested  and 
subjected  to  analysis.  The  following  are  some  of  the  results: 


Phosphoric  acid  in  Mgr. 
Per  vessel 

Weight  of  crop 
in  grams 

Phosphoric  acid 
in  dry  matter 
per  cent. 

Grain 

Straw 

5-8 
3-4 

2-7 

n 

1.8 

I.O 

0-3 

II.  0 

10.9 
II.  I 

10.2 

7-2 

5.2 
3.0 

I.I 

I.  II 

0.83 
0-53 
0-33 
0.28 
0.27 
0.27 
0.27 

33-°  
24  8  

TA  8 

1  Jahresber.  Agr.  Chem.,  1873,  p.  293. 


ESSENTIALS  OF  PLANT  LIFE  IQ 

When  the  plant  contained  less  than  0.33  per  cent,  of  phosphoric 
acid,  it  was  not  well  developed.  When  the  percentage  of  phos- 
phoric acid  was  increased  over  0.33  per  cent.,  the  quantity  of 
straw  was  little  affected,  but  the  quantity  of  grain  increased.  In 
the  presence  of  silica,  equally  as  much  grain  could  be  produced 
with  0.33  per  cent,  phosphoric  acid.  Wolff  therefore  concludes 
that  the  minimum  quantity  of  phosphoric  acid  required  by  the 
entire  oat  plant  is  0.33  per  cent,  of  the  dry  material. 

Similar  series  of  experiments  were  made  with  potash,  lime, 
and  other  forms  of  plant  food.  From  these  experiments  Wolff1 
concludes  that  the  minimum  requirements  of  the  oat  plant,  based 
on  the  dry  matter  of  the  entire  plant,  is  as  follows : — 

Per  cent. 

Phosphoric  acid 0.35 

Potash 0.8 

Lime o.  2 

Magnesia 0.2 

Sulphuric  acid 0.2 

Total  of  the  essential  constituents 1.75 

Pure  ash  necessary 3.00 

Nitrogen i.oo 

While  the  oat  plant  can  get  along  with  1.75  per  cent,  of  the 
essential  ash  constituents,  a  total  of  3.00  per  cent,  of  pure  ash 
is  absolutely  necessary.  It  was  impossible  to  grow  a  plant  with 
less  than  3.00  per  cent,  of  ash.  The  additional  1.25  per  cent, 
may  consist  either  of  essential  elements,  or  of  unessential  ele- 
ments, such  as  silica  or  soda,  but  the  quantity  required  must  be 
made  up  in  some  way  or  other.  We  may  term  the  ash  in  excess 
of  the  sum  of  the  essential  ash  ingredients,  the  indifferent  ash. 
The  unessential  elements  can  be  useful  to  the  plant  in  making 
up  its  indifferent  ash,  which  is,  however,  essential.  Various  sub- 
stances sometimes  added  to  the  soil,  such  as  salt,  gypsum,  lime, 
etc.,  may  be  useful  in  satisfying  the  need  of  the  plant  for  indiffer- 
ent ash.  Since  1.25  per  cent,  of  the  necessary  3.00  per  cent,  of 
the  ash  of  oats  may  be  of  varying  nature,  and  since  plants  may 
take  up  ash  in  excess  of  their  needs,  the  ash  of  the  plant  is 
subject  to  considerable  variation  in  composition. 
1  Jahresber.  Agr.  Chem.,  1875,  p.  251. 


2O  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Quantity  of  Plant  Food  Needed  by  Plants. — The  experiments 
by  Wolff  already  cited  show  the  minimum  requirements  of  the 
oat  plant,  but  this  method  has  not  been  applied  to  other  plants, 
and  we  are  dependent  upon  other  methods  for  ascertaining  the 
needs  of  the  plant.  The  only  other  method  which  has  been  used 
is  to  make  the  analysis  of  the  plant. 

This  is  not  altogether  a  safe  guide:  first,  because  plants  may 
take  up  an  excess  of  plant  food;  and  secondly,  near  maturity 
material  is  easily  washed  from  the  leaves  and  other  parts  of  the 
plant  by  rain,  dew,  etc.,  as  shown  by  LeClerc  and  Breazeale.1  For 
estimating  the  draft  of  the  plant  on  the  soil,  analysis  is  of  course 
more  satisfactory.  Such  analyses  are  also  used  for  calculating 
the  manurial  value  of  feeds.  Most  of  the  estimations  of  the 
mineral  matter  in  plants  have  been  made  by  analyses  of  the  ash. 
Nitrogen  is  determined  on  a  separate  sample  of  the  original  plant 
material. 

The  Ash  of  Plants. — When  plant  substance  is  burned,  the 
greater  portion  of  it  passes  off  as  volatile  bodies.  The  residue  is 
termed  the  ash.  The  ash  is  sometimes  spoken  of  as  the  mineral 
part  of  the  plant,  or  the  inorganic  part.  These  terms  are  not  cor- 
rect. The  ash  is  merely  that  portion  of  the  plant  which  forms 
compounds  not  volatile  at  the  temperature  of  the  combustion.  A 
portion  of  it  may  have  been  present  in  the  plant  in  the  form  of 
inorganic  bodies,  and  a  portion  has  undoubtedly  been  in  organic 
combination. 

The  term  crude  ash  is  applied  to  the  ash  as  secured  by  burning. 
Pure  ash,  or  carbon  free  ash,  is  the  crude  ash  less  the  free  carbon, 
carbon  dioxide,  and  sand  contained  in  it. 

Under  ordinary  conditions,  all  of  the  nitrogen  and  hydrogen, 
most  of  the  carbon  and  oxygen,  a  considerable  part  of  the  sul- 
phur, and  a  small  portion  of  the  potash  and  chlorine  pass  off  dur- 
ing combustion.  The  ash  consists  chiefly  of  carbonates,  oxides, 
sulphates,  phosphates,  silicates,  and  chlorides  of  potash,  lime, 
magnesia,  and  soda.  Unburned  carbon  is  usually  present,  and  in 
rare  cases  cyanides  and  sulphides  are  found.  The  fact  that  a 
1  Yearbook,  U.  S.  Department  Agriculture,  1908,  p.  389. 


ESSENTIALS  OF  PLANT 


21 


large  part  of  the  sulphur  is  volatilized  was  overlooked  for  a  long 
time.     For  example,  the  following  results1  were  obtained: — 


Percentage  of  SO3  in 

Cowpeas 

Corn 

0.08 
0.47 
84.0 

O.OI 

o-39 
97-0 

The  result  has  been  that  the  draft  of  the  plant  on  the  sulphur 
in  the  soil  has  been  decidedly  under-estimated,  and  it  is  quite 
possible  that  some  soils  may  be  deficient  in  sulphur.2 

Variations  in  Ash.3 — The  percentage  and  composition  of  the 
ash  of  plants  varies  according  to  the  kind  of  plant,  the  part  of 
the  plant,  the  stage  of  growth,  the  variety  of  the  plant,  the  soil, 
the  season,  and  other  conditions. 

Seeds  contain  plant  food  stored  for  the  benefit  of  the  young 
plant,  and  are  less  variable  in  composition  than  any  other  portion 
of  the  plant.  Although  they  contain  comparatively  small  quan- 
tities of  ash,  the  ash  is  rich  in  the  essential  plant  foods.  The 
pure  ash  is  composed  largely  of  phosphoric  acid,  from  30  to 
50  per  cent.;  potash,  about  30  per  cent.;  magnesia,  about  8  to 
15  per  cent.  Lime  is  present  in  comparatively  small  quantity, 
and  little  or  no  silica  is  found,  except  in  the  case  of  oats  or 
similar  plants  where  the  husk  or  chaff  is  included  in  the  analy- 
sis. (See  table  below).  Leguminous  seeds  appear  to  be  richer 
in  potash  and  poorer  in  lime  than  the  seed  of  cereals. 

Roots  and  tubers,  which,  like  seeds,  contain  a  reserve  store  of 
material  for  the  use  of  the  plant,  are  also  rich  in  valuable  plant 
food,  though  more  variable  in  composition  than  seeds.  Unlike 
seeds,  the  ash  carries  considerably  more  potash  than  phosphoric 
acid ;  but,  like  seeds,  it  contains  more  magnesia  than  lime. 

Leaves  of  plants  are  very  variable  in  composition.     The  ash 

1  Fraps,  Jour.  Am.  Chem.  Soc.,  23,  199. 

2  Jour.  Agr.  Sci.,  i,  p.  217. 

3  See   Wolff,    Ashen   Analysen.     Also  Tollens,    Exp.    Sta.    Record    13, 
pp.  207,  303. 


22 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


is  rich  in  potash  and  lime,  but  contains  much  smaller  quantities 
of  magnesia  and  phosphoric  acid.  The  quantity  of  silica  is  larger 
than  in  the  ash  of  seeds  or  tubers,  being  slightly  less  than  the 
phosphoric  acid. 

Cereal  straws  are  variable  in  ash  content,  though  the  ash  is  con- 
siderably lower  than  in  leaves.  The  ash  is  very  rich  in  silica,  and 
contains  fair  amounts  of  potash.  Its  content  of  lime  and  magnesia 
is  comparatively  small,  and  it  contains  about  half  as  much  phos- 
phoric acid  as  leaves.  Like  leaves,  cereal  straws  contain  more 
lime  than  magnesia. 

Leguminous  straws  resemble  leaves  closely.  The  ash  is  rich 
in  lime  and  potash,  and  contains  approximately  the  same  amounts 
of  phosphoric  acid  and  magnesia  as  the  ash  of  leaves. 

AVERAGE  AMOUNT  OF  ASH  CONSTITUENTS  IN  1000  PARTS  BY 
WEIGHT  OF  THE  DRY  SUBSTANCE. 


Number 
Aver- 
aged 

Pure 
ash 

Potash 

Ume 

Mag- 
nesia 

Phos- 
phoric 
acid 

Silica 

106 
7 
13 
113 

12 

17 

no 
36 
57 
57 
15 
3 
40 

18 
25 

38 

59 
149 

32 

Hay  and  Grasses  — 

69.8 
60.6 
23-6 
68.6 
73-8 
82.3 

19.6 
20.9 
26.1 
31.2 
14.5 
13-7 
27-3 
39-8 

53-7 
44-6 
7^-7 

37-9 

£? 

18.6 

21-5 
4.6 

22.2 

17.4 
25-4 

6.1 
6-7 
5-6 
5-6 
4-3 
3-2 
•ii.  8 
12.9 

7-3 

IO.I 
20.6 

22.8 
20.4 
36.4 

II.  I 
8.3 
i-9 
24.0 
30.0 
33-2 

0.6 
0.6 
0.7 
i.i 

°-3 
0.6 

1-3 

2.8 

3-i 
3-7 
5-o 

I.O 

i\ 

4.8 
6-5 

7-5 
3.6 
10.9 

2.4 

2.4 

2-3 

2.2 
2-3 
1-7 
2.2 
6.2 

L3 
1.4 
2.6 

1-9 

3-0 
3-o 

5-0 
6.1 
1.6 
6.6 
6-3 
5.o 

9-3 

10.0 

9.2 
8.0 
6.6 

6.7 
9-8 

13.9 

2.6 

2-9 

3-3 

6.4 

4.7 

10.2 

20.0 
I  I.O 
10.3 

i-9 
7.0 

0.9 

0.4 
0.3 
6.7 

12.2 
0-3 
0.3 
0-3 

0.6 

36.3 

22.0 

33-5 

0.8 
0.9 
1-5 

Green  corn  (in  bloom)  •  •  • 

Alfalfa  •  .           

Seeds  and  Fruits  — 

Oats  

Corn  

Buckwheat  

Ootton 

Straw— 
\Vinter  wheat  

Oats  • 

Roots  and  Tubers  — 
Potatoes 

ESSENTIALS  OF  PLANT 


Effect  of  the  Soil  and  Season. — The  character  of  the  soil  and 
the  weather  conditions  prevailing  during  the  growth  of  plants, 
have  a  great  influence  upon  the  composition  of  their  ash.  The 
seed  is  less  influenced  by  these  conditions,  but  the  straw  of 
cereals  is  greatly  affected.  Indeed,  it  has  been  proposed  to 
determine  the  needs  of  the  soil  for  plant  food  by  analysis  of 
certain  plants  grown  on  it. 

At  the  Rothamsted  Experiment  Station,  barley  has  been  grown 
on  a  certain  field  for  over  fifty  years.  Some  of  the  plots  receive 
no  fertilizer,  and  others  receive  various  mixtures,  but  the  treat- 
ment has  been  the  same  during  the  entire  period.  Plots  which 
do  not  receive  the  complete  fertilizer  should  be  depleted  of  the 
plant  food  not  added  in  the  fertilizer.  There  is  very  little  varia- 
tion in  the  composition  of  the  ash  of  the  grain.  The  phosphoric 
acid  and  silica  in  the  straw  vary  slightly,  but  great  changes  take 
place  in  the  percentages  of  potash  and  soda. 


Percentage  composition 
of  barley  ash,     grown 
40  years  without  potash1 

Potash 

Soda 

Average  10  years 
Average  10  years 
Average  10  years 
Average  10  years 
Average  40  years 

1852-61  

18.4 
13-3 
9-7 
7-4 
31.0 

6.4 
11.4 

12.7 
11.9 

2.2 

1862-71  

1872-81  

1882-91  

While  the  yield  of  grain  decreases  from  45.62  to  36.63  bushels 
per  acre,  the  composition  of  its  ash  is  little  affected.  The  potash 
in  the  ash  of  the  straw  decreases  from  18.4  per  cent,  to  7.4  per 
cent.,  accompanied  by  an  increase  in  soda,  though  not  in  cor- 
responding quantity.  The  ash  in  the  straw  from  the  plot  re- 
ceiving potash  fertilizers  contains  four  times  as  large  a  per- 
centage of  potash  as  ash  of  the  straw  produced  without  potash 
during  the  decade  1882-91.  Since  in  the  first  two  ten-year  periods 
about  2,700  pounds  straw  per  acre  was  produced  on  the  no-potash 
plot,  while  the  40  year  average  for  the  potash  plot  is  2587  pounds, 

1  Agricultural  Investigations  at  Rothamsted,  Gilbert,  Bulletin  22,  Office 
of  Exp.  Station,  U.  S.  Dept.  Agr.,  page  78. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


it  is  evident  that  the  higher  percentage  of  potash  did  not  con- 
tribute to  a  greater  production  of  straw.  That  is  to  say, 
plants  may  take  up  a  considerable  excess  of  plant  food,  especially 
of  potash.1 

The  influence  of  the  season  upon  the  ash  content  of  plants  is 
illustrated  by  the  same  series  of  analyses  referred  to  above, 
namely,  barley  grown  on  the  experimental  plots  of  the  Rotham- 
sted  Experiment  Station.  The  differences  between  the  average 
composition  of  the  ash  of  plants  from  plots  differently  manured, 
show  the  effect  of  ihe  application  of  plant  food.  The  differ- 
ences between  the  highest  and  lowest  content  of  ash  for  the  same 
manure,  show  the  effect  of  the  season.  The  results  in  the  follow- 
ing table  are  expressed  in  terms  of  the  plant  instead  of  the  ash  as 
in  previous  tables. 

EFFECT  OF  MANURES  AND  THE  SEASON  ON  POTASH  AND   PHOSPHORIC 
ACID  CONTENT  OF  BARLEY. 


Potash  and  phosphoric  acid  in  1000  parts  dry  matter 
of  the  plant- 

Potash 

Phosphoric  acid 

Highest 

Lowest 

Average 

Highest 

Lowest 

Average 

Grain  — 

7-7 
8.4 
8.0 

n.8 

22.O 
22.5 

6.0 

5-9 
5-6 

5-3 
6.8 

5-7 

6-5 
6.8 
6.6 

8.6 
13.2 
14.1 

10.  1 
10.5 
10.4 

2.6 

29 
3-1 

8.9 
9.2 
8.8 

1.2 

MB 

i.i 

9-3 

IO.O 

9.6 

i-7 

2.2 

i-9 

Farm  yard  manure.  .  . 
Complete  fertilizer.  .  . 

Straw— 

Farm  yard  manure-  •  . 
Complete  fertilizer.  .  . 

Both  fertilizer  and  season  have  comparatively  little  effect  upon 
the  composition  of  the  grain,  as  we  have  observed  before.  On 
the  straw,  the  season  has  a  greater  effect  than  the  fertilizer.  For 
example,  the  average  potash  in  the  unmanured  straw  is  to  the 
potash  in  the  manured  straws  as  8.60:14.10  or  less  than  1 :2,  while 
in  different  seasons  the  straw  grown  on  the  manured  plot  varied 

1  See  also  Wilfarth  and  Wimmer,  Exp.  Sta.  Record  13,  1030. 

2  Bulletin  22,  Office  of  Exp.  Station,  p.  75. 


ESSENTIALS  OF  PLANT  LIFE 


in  potash  from  6.8 :  22.00  or  over  I  :  3.  Inspection  of  the  table 
shows  that  phosphoric  acid  varies  in  a  similar  manner,  though 
the  variations  are  not  so  large.  In  these  experiments,  at  least, 
the  effect  of  the  season  is  greater  than  the  effect  of  fertilizers  or 
the  soil. 

Ash  of  Strong  and  Weak  Plants. — Various  chemists  have  select- 
ed strong  plants  and  weak  plants  growing  in  the  same  field  at  the 
same  time,  and  subjected  them  to  analysis.  Some  analyses  of 
this  kind  are  given  in  the  following  table1 : — 

COMPOSITION  OF  STRONG  AND  WEAK  PLANTS. 


Percentage  Composition  of  ash 

in  plant 

PotJish 

Lime 

Mag- 
nesia 

Oxide 
of  iron 

Phos- 
phoric 
acid 

Silica 

Winter  wheat  — 

Strong  plants  • 
Weak  plants  •  • 

8.04 

7-55 

43.07 
32.89 

6.40 
3-73 

3-60 
2.30 

0.20 
0.20 

7.08 
8.20 

32.82 
48.40 

Oats- 

Strong  plants  • 

8.03 

43-15 

7.02 

4-5° 

0.50 

7.28 

20.86 

Weak  plants  •• 

6.48 

39-35 

6.06 

3-30 

O.6o 

7.68 

34.18 

Barley- 

Strong  plants  . 

10.83 

43  10 

8.73 

3-83 

O.6o 

7.33 

18.67 

Weak  plants  .  . 

8.39 

38.15 

7-33 

3-77 

O.6o 

8.20 

30.50 

The  weak  plants  contain  a  smaller  percentage  of  ash  than  the 
strong  plants.  The  percentages  of  potash  and  lime  are  smaller, 
and  the  percentages  of  silica  are  much  larger  in  the  ash  of  the 
weak  plants. 

Effect  of  Stage  of  Growth  on  Ash. — The  percentage  of  ash 
shows  the  relation  between  the  organic  matter  formed  and  min- 
eral matter  taken  up  by  the  plant.  The  absorption  of  mineral 
matter  from  the  soil,  and  the  production  of  organic  matter  by  the 
plant,  do  not  proceed  at  the  same  rate,  consequently  the  per- 
centage of  ash  in  the  plant  varies  at  different  periods  of  time. 
Changes  in  the  ash  content  of  plants  at  different  periods  of 
growth  depend  upon  the  kind  of  plant,  and  the  part  of  the  plant 
under  consideration.  As  a  general  rule,  we  find  that  the  ash  con- 
tent is  greatest  in  the  young  plant,  and  that  it  decreases  with  the 
1  Wolff's  Ashen  Analysen. 
3 


26 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


age  of  the  plant.  That  is  to  say,  the  young  plant  takes  up  more 
mineral  matter  in  proportion  to  the  quantity  of  organic  matter  it 
elaborates,  than  the  older  plant. 

The  nature  of  the  soil  also  affects  the  changes  in  the  ash  of 
a  plant  during  its  growth.  When  an  insufficient  quantity  of  plant 
food  is  supplied  by  the  soil,  the  plant  may  withdraw  ash  ingre- 
dients from  its  older  parts  for  use  in  continuing  its  growth.  As 
we  have  seen,  in  the  presence  of  an  excess  of  plant  food,  the 
plant  may  take  up  more  ash  than  it  needs.  These  facts  should 
be  borne  in  mind  in  considering  the  changes  in  the  ash  ingre- 
dients during  the  growth  of  plants.  The  composition  of  the 
plant  at  different  stages  on  one  soil,  under  one  set  of  conditions, 
may  be  quite  different  from  the  same  plant  grown  on  another 
soil  under  another  set  of  conditions.  When  the  plant  approaches 
maturity,  ash  may  be  washed  out  by  rain. 

For  the  reasons  just  given,  the  following  general  statements 
may  not  apply  to  individual  cases.  With  the  entire  plant,  the 
percentage  of  potash  in  the  ash  decreases  almost  invariably, 
while,  as  a  rule,  silica  increases,  magnesia  increases,  lime  de- 
creases, and  phosphoric  acid  decreases  in  some  cases  and  in 
others  increases. 

The  above  statements  are  made  with  respect  to  the  entire  plant. 
Exceptions  occur  with  certain  parts  of  the  plant,  as,  for  example, 
the  ears  of  oats. 

An  example  is  presented  in  the  following  table.  Samples  of 
the  entire  wheat  plant  were  collected  at  different  periods  of 
growth  and  subjected  to  analysis  by  Pierre:1 

EFFECT  OF  STAGE  OF  GROWTH  ON  ASH  OF  PLANTS. 


Stage  of  growth 

Pure  ash 
in  plant 
Per  cent. 

Percentage  composition  of  ash 

Potash 

Lime 

Mag- 
nesia 

Phos- 
phoric 
acid 

Silica 

74 
6-5 
5-3 
5-1 
48 

4-7 

22.8 
'5-2 
13-5 
13.0 
10.2 
10.2 

20.7 
17-5 
13-7 
II.  5 
12.4 
10.  T 

3-8 
4.2 
2.7 
2.7 
2.2 
2.4 

IO.I 

9-i 
6.1 

5-6 
5-3 
5-9 

35-2 
45-0 
55-9 
58-3 
62.5 

64.7 

Beginning  of  bloom  

Ripe            

1  Wolff's  Ashen  Analysen. 


ESSENTIALS  OF  PLANT 


As  the  grain  ripens,  and  the  proportion  of  seed  to  husk 
increases,  a  decrease  in  the  percentage  of  silica  in  the  ash  occurs. 

Ratio  of  the  Essential  Elements. — The  ratio  of  the  essential 
elements  affects  the  development  of  the  plant  to  some  extent. 
Director  Hall1  of  the  Rothamsted  Station  states  that  where 
barley  is  grown  on  the  plots  fertilized  with  potash  and  nitrogen 
without  phosphoric  acid,  the  grain  hardly  matures  at  all,  while 
the  phosphoric  acid  in  the  absence  of  nitrogen  and  potash  causes 
the  grain  to  ripen  early. 

Starting  with  the  fact  that  lime  predominates  in  leaves  while 
magnesia  is  in  excess  in  seeds,  May,  under  the  direction  of 
Loew,2  grew  tobacco  in  sand  culture  with  excess  of  lime  and 
with  excess  of  magnesia,  producing  in  the  first  experiment  a 
large  development  of  leaves,  in  the  second  a  very  small  plant. 
According  to  other  experiments  of  Loew  and  his  pupils,  the 
ratio  of  lime  to  magnesia  is  of  importance. 

For  example,  Aso3  grew  rice  with  various  ratios  of  lime  to 
magnesia.  The  lime  and  magnesia  originally  in  the  soil  were 
estimated  by  extracting  the  soil  for  24  hours  with  cold  10  per 
cent,  hydrochloric  acid.  Such  additions  of  carbonate  of  lime 
or  carbonate  of  magnesia  were  then  made  to  various  pots  con- 
taining 7  kilograms  of  the  soil  as  were  necessary  to  secure  the 
desired  ratios  of  lime  to  magnesia.  In  order  to  ensure  an 
abundance  of  plant  food,  each  pot  also  received  15  grams 
ammonium  sulphate,  15  grams  sodium  phosphate,  and  15  grams 
potassium  carbonate. 

The  following  are  the  results  of  this  experiment : 


Ratio  of  lime  to  magnesia 

Weight  of 
grain  in  grams 

Weight  of 
straw  in  grams 

2o  ^ 

C-y    r 

.  i  •  ' 

•JQ  r 

06-0 

CQ    C 



.  i  •  • 

OUO 

A  A    O 

59-5 
6c  e 

2           

<;8  ^ 

05-5 
DQ  O 

j            

S°'5 
08  «; 

TO?  O 

j       2   

84  o 

QC  o 

I       1   .  . 

7O  O 

yo-^ 
106  o 

/y.«~» 

1  Rothamsted  Experiments,  p.  80. 

2  Bulletin  No.  I,  Bureau  Plant  Industry,  U.  S.  Dept.  Agr. 

3  Bulletin  Tokyo  Imp.  Uni.,  1904,  p.  97. 


28 


PRINCIPLES  OF  AGRICULTURAL,  CHEMISTRY 


According  to  this  experiment,  the  ratio  of  i  part  lime  to  i  part 
magnesia  is  most  favorable  to  the  growth  of  rice.  An  increase 
or  decrease  in  the  ratio  reduces  the  yield,  an  excess  of  lime  being 
more  injurious  than  any  excess  of  magnesia. 


Fig.  3. — Upper  tobacco  plant  has  excess  of  magnesia,  lower  plant 
excess  of  lime.     Loew.     U.  S.  D.  A. 


In  other  experiments  Loew1  found  the  most  favorable  ratio  of 
lime  to  magnesia  for  some  other  plants  to  be  as  follows : — 

1  Bui.  Col.  Agr.  Imp.  Univ.  Tokyo,  1902,  p.  381. 


ESSENTIALS  OF  PLANT  LIFE  2Q 

Lime  :  Magnesia  :  :   i  :   I    for   oats, 
:  :  2  :   i  for  barley, 
1:3:1  for  wheat. 

Lime,1  he  says,  is  required  for  foliage,  and  magnesia  for  seed; 
the  greater  the  proportion  of  foliage  to  seed,  the  greater  the  ratio 
of  lime  to  magnesia  required  by  the  plant. 

Several  factors  operate  to  prevent  injury  by  an  unfavorable 
ratio  of  plant  food  in  the  soil.  The  root  of  the  plant  exercises  a 
certain  degree  of  selection  by  which  it  may  to  some  extent  de- 
cline to  absorb  undesirable  plant  food.  In  some  plants  an  excess 
of  lime  is  deposited  in  cells  in  the  form  of  calcium  oxalate,  in 
others,  it  forms  a  white  coating  (probably  carbonate  of  lime) 
upon  the  leaves.  There  is  a  difference  of  opinion  as  to  the 
significance  of  Loew's  work.  According  to  Hopkins'  experi- 
ments,2 the  quantity  of  lime  and  magnesia  are  of  more  importance 
than  the  ratio. 

The  importance  of  the  ratio  of  lime  to  magnesia  in  practical 
farming  remains  to  be  decided  by  field  experiments. 

Plant  Stimulants. — Substances  which  exert  an  appreciably 
favorable  action  upon  plant  growth  and  at  the  same  time  are  not 
essential  to  the  life  of  the  plant,  may  be  termed  stimulating  com- 
pounds. According  to  Loew3  and  his  pupils,  borax  and  salts  of 
lithium,  caesium,  uranium,  manganese,  bromine,  iodine,  fluorine, 
and  ferrous  iron  act  as  plant  stimulants  in  small  doses ;  in  large 
quantities,  they  may  prove  injurious.  The  more  important 
of  these  stimulants4  appear  to  be  manganese,  iron,  and 
fluorine.  It  is  also  possible  that  certain  organic  substances 
may  act  as  stimulants  in  small  doses,  or  as  poisons  in  large 
doses.  According  to  Loew,  the  favorable  quantity  of  the  stimu- 
lants named  is  as  follows : — Manganous  sulphate  about  75  pounds 

1  See  also  Circ.  No.  10,  Porto  Rico  Exp.  Sta.  :  Bui.  45,  Bureau  of  Plant 
Industry. 

2  Soil  Fertility  and  Permanent  Agriculture,  p.  170. 

3  Bui.  Tokyo  Univ.,  1904,  p.  163. 

4  Int.  Cong.  App.  Chem.,  1912,  15,  p.  39. 


3<3  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

per  acre;  manganous  chloride  60  pounds;  potassium  iodide  one- 
third  ounce;  sodium  fluoride  one  ounce. 

The  importance  of  these  stimulating  compounds  in  practical 
agriculture  remains  to  be  demonstrated.  Such  field  tests  as  have 
come  to  the  notice  of  the  writer  are  contradictory.  It  has  been 
suggested  that  the  copper  hydroxide  and  similar  substances  used 
for  combating  certain  plant  diseases,  instead  of  killing  the  fungus 
direct,  stimulate  the  plant  and  increase  its  vigor  sufficiently  to 
resist  the  disease,  but  we  know  of  no  experiments  supporting  this 
hypothesis.  It  is  also  possible  that  "stimulating"  compounds  may 
occur  in  certain  soils  in  quantity  sufficient  to  be  injurious. 

Essentials  for  Plant  Life  in  Addition  to  Food. — Conditions  other 
than  plant  food  which  are  essential  to  plant  life  are 
mentioned  here  for  the  sake  of  completeness.  The  requirements 
of  foliage,  fruit,  or  roots  are  different,  but  the  entire  plant  suffers 
if  a  part  suffers. 

Water,  in  considerable  quantity,  is  essential  to  plant  life.  Only  a 
small  portion  of  the  water  used  by  a  plant  is  used  as  plant  food 
and  goes  to  the  formation  of  organic  material.  Most  of  it  is 
evaporated  by  the  leaves  of  the  plant. 

Light  is  essential  to  the  formation  of  organic  matter  by  the 
leaves  of  plants.  Too  much  or  too  little  light  affects  the  develop- 
ment of  the  plant.  Plants  vary  in  their  requirements  for  light. 

Temperature. — Extremes  of  heat  and  of  cold  destroy  plants. 
For  their  best  growth  a  certain  temperature  is  most  favorable, 
and  it  varies  with  the  kind  of  plant.  Temperatures  which  do  not 
destroy  the  plant  may  yet  interfere  with  its  growth. 

Favorable  soil  conditions  are  essential ;  the  proper  degree  of 
moisture,  of  soil  atmosphere,  absence  of  deleterious  influences, 
etc.,  are  necessary  to  the  best  growth. 

The  Law  of  Minimum. — In  the  experiment  of  Wolff  on  oats, 
cited  previously,  the  size  of  the  oat  crop  varied  with  the  quantity 
of  phosphoric  acid  supplied  to  it,  other  conditions  being  favor- 
able. In  the  following  experiment  of  Hellriegel,1  various 
1  Exp.  Station  Record,  1893-4,  p.  853. 


ESSENTIALS  OF  PLANT 


Grams  dry  matter 
produced 
per  pot 


quantities  of  nitrogen  were  added  to  a  soil  provided  with  an 
abundance  of  all  other  forms  of  plant  food,  all  other  conditions 
being  favorable.  The  harvest  of  the  barley  gave  the  following 
results : — 

Grams  nitrogen 
supplied 
per  pot 

O.OOO 0.50 

0.028 2.99 

0.056 5.32 

O.I  12 I0.8o 

o.  168 16.38 

0.224 21.72 

The  size  of  the  crop  increases  with  the  quantity  of  nitrogen  at 
the  disposal  of  the  plant.  The  size  of  the  crop  thus  varies  with 
the  quantity  of  the  most  deficient  form  of  plant  food.  The  plant 
food  is  the  controlling  condition  in  these  experiments.  Plant 
food,  however,  is  only  one  requirement  of  plant  life.  The 
amount  of  the  crop  is  profoundly  influenced  by  rainfall,  tempera- 
ture, and  other  weather  conditions  which  are  embraced  under  the 
term  season,  as  well  as  by  the  nature  of  the  soil,  etc. 


Fig.  4.— The  growth  of  oats  is  proportional  to  the  supply  of  nitrate 
of  soda,  other  conditions  being  favorable  (after  Wagner). 

The  law  of  minimum  holds  that  the  size  of  the  crop  is  regu- 
lated by  the  condition  least  favorable  to  the  growth  of  the  plant. 


32  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

For  instance,  suppose  all  conditions  were  favorable  to  the  produc- 
tion of  100  bushels  of  corn,  with  the  exception  of  phosphoric 
acid ;  then  the  size  of  the  crop  would  depend  upon  the  quantity  of 
phosphoric  acid  it  could  secure;  if  only  enough  for  10  bushels, 
then  ten  bushels  it  would  be.  Suppose  the  soil  were  very  rich,  as 
it  often  is  in  arid  regions,  and  there  were  little  water,  then 
quantity  of  water  would  limit  the  size  of  the  crop.  An  excess 
of  water  would  also  limit — decrease — the  crop.  If  all  conditions 
of  soil  and  water  were  favorable,  the  limiting  conditions  might  be 
the  quantity  of  light  the  plant  received,  the  temperature,  or  the 
individuality  of  the  plant. 

The  conditions  which  limit  plant  growth  may  be  kind  of  seed, 
light,  water,  space,  temperature,  total  ash,  phosphoric  acid  or  any 
other  plant  food,  insects,  injurious  diseases,  or  the  condition, 
nature  or  situation  of  the  soil.  The  size  of  the  crop  depends 
upon  the  least  favorable  of  the  conditions  which  surround  it.  It 
is  exceedingly  important  in  practical  agriculture  to  ascertain  the 
limiting  conditions,  and  render  them  more  favorable. 

Mitscherlich1  gives  mathematical  expression  to  the  law  of 
minimum.  Under  ideal  conditions,  a  certain  maximum  yield 
would  be  obtained.  The  yield  is  depressed  if  some  essential 
factor  is  deficient.  If  now  the  deficiency  is  overcome  to  a 
certain  extent,  the  yield  becomes  greater,  and  is  the  larger,  the 
greater  the  previous  depression.  According  to  Mitscherlich,  the 
increase  in  crop  produced  by  a  unit  increment  of  the  lacking 
factor  is  proportional  to  the  decrement  from  the  maximum. 
The  mathematical  expression  is : 

dy 
-fe  =  (A  —  y}k  or  loge(A  —  y}  =  c  —  kx. 

When  x  is  the  amount  of  the  factor  present,  y  is  the  yield,  and 
A  is  the  maximum  yield  possible  with  an  excess  of  the  factor. 

Permanent  and  Variable  Limiting  Conditions. — The  character 

of  the  soil  and  the  plant  food  which  it  supplies  are  more  or  less 

permanent  during  the  growth  of  the  crop,  but  the  soil  moisture 

and  the  weather  conditions  are  more  variable.    The  limiting  con- 

1  Landw.  Versuchs-stat.,  1911,  p.  231. 


ESSENTIALS  OF  PLANT 


33 


editions  of  plant  growth  are  therefore  more  or  less  variable, 
according  as  moisture  or  weather  conditions  are  more  or  less 
favorable  to  growth  than  are  soil  conditions.  The  rate  of  growth, 
for  example,  may  at  one  time  be  controlled  by  the  phosphoric 
acid  supply  of  the  soil,  and  at  another  by  decrease  in  the  rate  of 
supply  of  moisture  (drought)  or  by  an  excess  of  water  or  by  too 
cool  a  temperature,  or  too  little  sunlight,  etc.  The  conditions  of 
the  soil  and  its  supply  of  plant  food  are  more  or  less  affected  by 
soil  moisture,  weather,  or  other  conditions. 

The  varying  effect  of  the  season  upon  plots  with  different 
fertilizer  applications,  may  be  seen  by  comparing  the  yield  of 
wheat  in  a  wet  year  and  in  a  dry  year,  with  the  average  for  51 
years,  on  the  plots  at  Rothamsted,1  England. 


Treatment 

Yield  of  wheat  in  bushels  per  acre 

Average 

Wet  year 

Dry  year 

I3-I 
14.9 

24.0 
33-8 
20.7 
22.7 
35-7 

4-5 
5-6 

10.5 
17.9 
4-3 
4-6 
16.0 

10.7 
14.2 

19.4 
21.9 

8.4 

10.0 

34-2 

Acid  phosphate,    potash    salts,    sulphate    of 

There  is  nearly  as  much  difference  between  the  average  crop 
on  the  farm-yard  manured  plot,  and  the  crop  during  the  wet 
season,  as  there  is  between  the  average  yield  with  no  addition, 
and  with  the  farm-yard  manure. 

Limiting  Conditions  are  Dependent  Variables. — The  limiting 
conditions  are  not  independent  of  one  another,  but  to  a  certain 
extent  influence  each  other  so  that  variation  in  one  may  affect 
several.2  Increase  in  water  in  the  soil,  for  example,  decreases  the 
air  content,  and  may  decrease  soil  temperature.  By  transpiring 
more  water,  the  plant  can  take  up  more  plant  food.  Increase  in 
phosphoric  acid  of  the  soil  may  also  increase  the  activity  of  the 

1  Hall,  an  account  of  the  Rothamsted  Experiments,  p.  54. 

'2  Cameron,  Proc.  Am.  Soc.  Agron.,  1910,  p.  102. 


34  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

soil  bacteria,  those  which  convert  inert  organic  matter  into 
nitrates  included,  and  thus  increase  the  supply  of  plant  food. 
The  phosphate  added  may  affect  the  physical  character  of  the 
soil.  Increase  in  the  soluble  plant  food  in  the  soil  decreases  the 
need  of  the  plant  for  water  and  its  transpiration  becomes  less. 
Increase  in  temperature  increases  the  action  of  soil  moisture 
upon  plant  food  constituents,  and  increases  the  activity  of  the 
soil  organisms.  Thus  a  change  in  one  condition  of  plant  life 
may,  and  usually  does,  affect  more  than  one,  and  the  conditions 
are  not  absolutely  independent. 


CHAPTER  III. 


THE  PLANT  AND  THE  ATMOSPHERE. 

Although  the  atmosphere  is  equally  as  important  as  the  soil  for 
the  production  of  plants,  yet,  since  atmospheric  conditions  are 
little  subject  to  control  and  are  less  complex  in  relation  to  the 
plant  than  soil  conditions,  much  less  attention  need  be  given  to  it. 
We  have  already  found  that  the  carbon  of  the  plant  comes  from 
the  air.  The  atmosphere  receives  and  transports  water  vapor, 
and  precipitates  it  in  the  form  of  rain  or  snow.  The  amount, 
kind  and  period  of  rainfall  which  are  dependent  on  atmospheric 
conditions  are  highly  important  to  agriculture.  The  atmosphere 
moderates  the  variations  in  temperature.  It  tempers  and  stores 
the  heat  of  the  sun.  If  there  were  no  atmosphere,  the  tempera- 
ture would  be  very  hot  in  the  direct  sunshine  and  freezing  in  the 
shade. 

The  soil  atmosphere  is  also  of  importance.  The  air  penetrates 
the  soil,  supplies  the  roots  of  plants  with  the  oxygen  they  need, 
and  oxidizes  deleterious  substances.  It  aids  in  the  preparation 
of  plant  food  so  that  the  plant  can  take  it  up.  It  also  aids  in  the 
formation  of  soil  from  rock. 

Composition  of  the  Air. — The  air  consists  chiefly  of  nitrogen 
and  oxygen.  It  contains,  in  addition,  a  small  amount  of  carbon 
dioxide,  some  water  vapor,  small  quantities  of  argon  and  allied 
rare  gases,  besides  minute  quantities  of  ammonia,  nitric  acid, 
hydrogen  peroxide,  and  marsh  gas.  It  also  contains  suspended 
solid  matter,  some  of  which  consists  of  micro-organisms. 
In  towns,  the  air  contains  some  sulphuric  acid  and  hydrogen  sul- 
phide. The  moisture  in  the  air  varies  considerably. 

The  composition  of  dry  air  varies  but  slightly,  even  when 
sampled  at  widely  distant  localities.  Its  average  composition  by 
volume  is  as  follows : — 

Oxygen 20.90  parts. 

Argon 0.90  parts. 

Nitrogen 78. 15  parts. 

Carbon  dioxide 0.03  parts. 

Hydrogen 0.02  parts. 

100.00  parts. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Carbon  Dioxide.  —  If  a  vessel  of  clear  lime  water  is  exposed  to 
the  air,  the  lime  water  after  a  time  becomes  cloudy,  and  a  white 
precipitate  or  a  crust  of  calcium  carbonate  is  formed.  The 
formation  of  this  precipitate  is  a  test  for  carbon  dioxide,  and  it  is 
due  in  this  case  to  the  carbon  dioxide  of  the  air  : 


Ca(OH) 


CO2  =  CaCO3 


HO. 


Since  plants  can  be  grown  to  full  maturity  in  water  containing 
certain  mineral  salts,  and  the  plant  contains  much  more  carbon 
than  the  seed,  while  the  water  does  not  contain  any,  it  followrs 
that  the  plant  must  have  taken  carbon  from  the  air. 

The  following  is  an  example  of  an  experiment  showing  that 
plants  can  assimulate  carbon  dioxide  in  the  presence  of  light. 
Boussingault  placed  a  sprig  of  leaves  in  a  vessel  containing  86.5  cc. 
of  a  mixture  of  oxygen  and  carbon  dioxide  and  exposed  it  to  the 
sun.  After  nine  hours  exposure,  the  gas  was  measured  and  sub- 
jected to  analysis.  The  results  of  the  experiment  follow:  — 


Carbon  dioxide 

Oxygen 

31.9  cc. 
12.3  cc. 

11.5  cc. 
3I.4CC. 

Loss  

19.6  cc. 

Gain  19.9  cc. 

This  shows  that  the  leaves  absorbed  carbon  dioxide  and  re- 
placed it  with  a  nearly  equal  volume  of  oxygen. 

Another  experiment  consists  in  enclosing  the  plant  in  an  air- 
tight vessel,  through  which  air  is  passed.  A  known  amount  of 
carbon  dioxide  is  added  to  the  air,  and  the  carbon  dioxide  in  the 
air  which  passes  out  is  determined.  The  quantity  which  dis- 
appears is  absorbed  by  the  plant.  Numerous  experiments  give 
the  same  results.  7'he  green  leaves  of  plants  absorb  carbon 
dioxide  in  the  presence  of  light,  and  replace  it  with  an  equal  or 
nearly  equal  volume  of  oxygen. 

The  amount  of  carbon  dioxide  in  the  air  can  be  estimated  by 
drawing  a  known  volume  of  air  first  through  calcium  chloride  to 
remove  water,  and  then  through  a  solution  of  caustic  potash  to 


THE;  PLANT  AND  THE:  ATMOSPHERE:  37 

absorb  the  carbon  dioxide.  The  potash  bulb  is  weighed  before 
and  after  the  experiment,  and  the  gain  in  weight  is  carbon  dioxide. 
The  carbon  dioxide  may  also  be  absorbed  by  soda-lime,  or  by 
barium  hydroxide.  Water  lost  from  the  absorbing  tube  is  col- 
lected in  a  small  tube  containing  calcium  chloride,  and  weighed 
with  the  absorbing  tube. 

While  the  percentage  of  carbon  dioxide  in  the  air  is  small,  and 
is  continually  depleted  by  plants  during  the  day,  yet  the  total 
quantity  is  large.  The  income  and  outgo  of  the  carbon  dioxide  of 
the  air  appear  so  nearly  to  balance  that  no  great  variation  in  the 
amount  takes  place.  The  following  are  the  chief  processes  which 
restore  carbon  dioxide  to  the  atmosphere :  - 

(1)  The  respiration  of  animals.     Animals  absorb  oxygen  and 
give  off  carbon  dioxide.     The  oxidation  of  organic  material  de- 
rived from  food  or  body  substances  produces  the  carbon  dioxide. 

(2)  Combustion.     All  processes  of  combustion  of  organic  ma- 
terials produce  carbon  dioxide. 

(3)  Fermentation  and  decay.     These  are  changes  which  occur 
in  organic  materials,  and  are  usually  accompanied  by  production 
of  carbon  dioxide. 

(4)  Decomposition  of  calcium  bicarbonate  by  shell  fish.     The 
calcium  bicarbonate  dissolved  in  the  sea  water  is  decomposed, 
setting  carbon  dioxide  free,  and  the  calcium  carbonate  is  used  by 
the  animal  to  form  its  shell. 

Ca(HCO3)2  =  CaCO3  +  H2O  +  CO2. 
This  carbon  dioxide  was  originally  derived  from  the  air. 

(5)  Dissociation  of  carbonates  by  heat,  as  in  the  burning  of 
lime.     This  is  a  matter  of  small  importance,  especially  as  the 
lime  takes  up  the  carbon  dioxide  again  sooner  or  later. 

CaCO3  =  CaO  +  CO,2 

Carbon  dioxide  is  also  emitted  from  some  volcanoes,  deep 
springs,  and  other  subterranean  sources. 

Quantity  Present. — Country  air  contains  on  an  average  0.029 
per  cent,  carbon  dioxide,  or,  in  round  numbers,  3  volumes  to 
10,000  volumes  of  air.  City  air  contains  larger  quantities.  Angus 


38  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Smith  found  the  air  in  Glasgow  to  contain  0.05  per  cent,  and  in 
London  0.044  per  cent.  More  carbon  dioxide  is  present  in  the 
air  at  night  than  in  the  day.  For  example,  Armstrong1  found 
the  air  to  contain  0.0296  per  cent,  carbon  dioxide  in  the  day,  and 
0.330  per  cent,  at  night. 


CARBON D/OX/DE  OF  Am 


Off&AN/C 

GARBONOF 
PLANTS 


Fig.  5. — Circulation  of  carbon. 

These  variations  are  easily  explained.  In  cities  more  carbon 
dioxide  is  evolved  by  respiration  and  combustion  than  in  the 
country,  and  less  is  absorbed  by  plants.  At  night  the  production 
of  carbon  dioxide  by  animals  continues,  but  plants  give  it  off 
instead  of  absorbing  it,  hence  the  larger  amount  at  night. 
1  Proc.  Roy.  Soc.,  1880,  p.  343. 


THE;  PLANT  AND  THE:  ATMOSPHERE;  39 

Carbon  dioxide  is  soluble  in  water,  and  is  brought  to  the  earth 
with  rain.  It  exerts  a  solvent  action  on  constituents  of  soils  and 
rocks,  especially  on  carbonate  of  lime.  The  amount  of  carbon 
dioxide  dissolved  by  water  varies  according  to  temperature  and 
pressure.  Carbon  dioxide  is  usually  found  in  springs,  wells,  and 
river  water,  as  well  as  in  dew  or  rain. 

Circulation  of  Carbon. — Carbon  circulates  from  the  air  to 
plants,  from  plants  to  animals,  and  from  plants  and  animals  back 
to  the  air.  The  oxidation  of  carbon  in  decay  of  organic  matter 
is  due  to  bacteria.  The  diagram  on  page  38  illustrates  the  cir- 
culation of  carbon. 

Effect  of  Light  on  Plants. — The  energy  stored  by  plants  comes 
for  the  most  part  from  the  sunlight.  In  the  presence  of  light, 
green  leaves  absorb  carbon  dioxide  and  give  off  oxygen.  This 
can  be  demonstrated  by  a  simple  experiment.  Some  fresh  green 
leaves  are  placed  in  a  funnel  filled  with  water  containing  carbon 
dioxide,  inverted  in  a  vessel  of  water,  and  placed  in  the  sunlight. 
Bubbles  of  gas  begin  to  rise,  which  may  be  collected  in  a  small 
test-tube  attached  to  the  stem  of  the  funnel,  and  tested  with  a 
spark  on  a  splinter.  This  bursts  into  flame,  and  so  proves  the 
gas  to  be  oxygen. 

In  darkness,  plants  take  up  oxygen  and  give  off  carbon  dioxide, 
though  the  amount  is  small  in  comparison  with  the  reverse  action 
in  the  light.  For  example,  Corenwinder1  ascertained  that  three 
pea  plants  exhaled  24  cc.  carbon  dioxide  during  an  entire  night, 
while  they  absorbed  86  cc.  carbon  dioxide  during  an  hour  of 
direct  sunshine. 

The  amount  of  light  most  favorable  to  the  growth  and  develop- 
ment of  the  plant,  depends  on  the  kind  of  plant.  Some  plants 
grow  better  in  the  sunshine,  while  others  thrive  only  in  the 
shade.  In  the  diffused  light  of  cloudy  days,  or  the  softened  light 
of  a  forest,  plants  may  exhale  either  carbon  dioxide  or  oxygen, 
according  to  the  kind  of  plant,  the  intensity  of  the  light,  and  the 
stage  of  development  of  the  plant. 

Chlorophyll,  the  green  coloring  matter  of  the  leaf,  seems  to 
1  Jahresber  Agr.  Chem.,  1858,  p.  106. 


40  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

be  an  essential  agent  in  the  decomposition  of  carbon  dioxide  and 
the  production  of  organic  matter.  Only  those  parts  of  the  plant 
which  contain  chlorophyll  are  able  to  assimilate  carbon  dioxide. 
If,  for  any  reason,  chlorophyll  is  not  formed,  assimilation 
cannot  take  place.  The  green  color  of  chlorophyll  is  sometimes 
disguised  by  the  presence  of  other  pigments. 

Effect  of  Color  of  Light. — The  effect  of  light  depends  upon  its 
color  and  intensity.  The  following  are  outlines  of  methods  for 
studying  the  effect  of  color  of  light  on  plants. 

(i)  Plants  may  be  grown  in  boxes  of  different  colored  glass.1 
This  method  allows  the  experiment  to  be  continued  any  desired 
length  of  time.  The  plants  can  be  then  subjected  to  analysis  or 
otherwise  examined.  The  light  which  passes  through  colored 


Fig.  6. — Tent  for  shading  tobacco.     Pennsylvania  station, 
glass,  is  not,  however,  usually  a  single  color,  but  is  admixed  with 
white  or  other  colors,  as  can  be  easily  seen  by  analysis  of  it  with 
a  spectroscope.     This  is  an  objection  to  the  method. 

(2)  A  ray  of  sunlight  is  decomposed  with  a  prism  and  the 
spectrum  thrown  upon  a  screen  with  a  slit  in  it,  allowing  the 

1  Weber,  Jahresber.  f.  Agr.  Chem.,   1875-6,  p.  336.      Flammarion,  Exp. 
Sta.  Record  10,  p.  103. 


THE:  PLANT  AND  THE:  ATMOSPHERE 


Fig.  7.— Tobacco,  (A)  shaded;  (B)  not  shaded.     Pennsylvania  Station. 


42  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

passage  of  only  one  kind  of  light.  This  falls  upon  a  leaf  placed 
in  water  containing  carbon  dioxide.  All  the  colors  except  the  one 
to  be  tested  are  excluded  by  the  screen.1  The  number  of  bubbles 
of  oxygen  liberated  from  the  leaf  in  a  given  time  is  taken  as  a 
measure  of  the  action  of  the  light  in  producing  organic  matter  by 
the  decomposition  of  carbon  dioxide.  More  accurate  results  are 
secured  if  the  volume  of  oxygen  is  measured. 

Control  of  Light. — Only  in  isolated  cases  is  control  of  light  of 
practical  significance  in  agriculture.  Forcing  of  early  vegetables 
by  artificial  light  has  been  tried  but  has  not  proved  successful 
enough  to  be  generally  adopted.  Cigar  wrapper  tobacco  is  grown 
under  the  shade  of  cheesecloth  or  slats.2  Reduction  of  light  by 
shading  makes  the  plant  grow  taller  and  produce  thinner  leaves 
than  under  ordinary  conditions.  The  thin  leaves  bring  high 
prices  for  use  as  wrappers  in  making  cigars.  The  shading,  how- 
ever, also  modifies  moisture  and  temperature  conditions.3 

Oxygen. — Oxygen  is  necessary  to  both  animal  and  plant  life. 
Without  oxygen,  animals  quickly  die  from  suffocation.  The 
oxygen  is  required  by  animals  for  processes  of  oxidation 
necessary  to  life,  such  as  the  production  of  animal  heat.  The 
oxygen  consumed  is  replaced  by  carbon  dioxide  in  the  respired 
air.  Oxygen  is  also  consumed  in  the  decay  of  organic  matter,  in 
combustion,  and  in  other  processes  of  oxidation. 

The  oxygen  lost  from  the  air  by  oxidation  is  restored  by  green 
plants,  which,  as  we  have  seen,  absorb  carbon  dioxide  and  evolve 
oxygen.  On  account  of  diffusion  and  air  currents,  the  quantity 
of  oxygen  in  the  air  varies  but  slightly.  In  analyses  made  in 
widely  separated  parts  of  the  world,  the  minimum  and  maximum 
amounts  of  oxygen  in  pure  dry  air  are  20.53  an<^  2I-°3  parts  by 
volume. 

Oxygen  is  necessary  for  the  germination  of  seeds,  for  the 
development  of  buds,  for  the  roots  of  certain  plants,  and  for 

1  Pfeffer,  Jahresber  Agr.  Chem.,  1870-2,  p.  179. 

2  Report  No.  62,  U.  S.  Dept.  Agr. 

3  Stewart,  Bui.  39,  Bureau  of  Soils. 


THE:  PLANT  AND  THE  ATMOSPHERE  43 

flowers.  De  Saussure1  found  that  buds  require  oxygen  by  the 
following  experiment.  He  enclosed  woody  twigs  cut  in  the  spring 
just  before  the  time  for  buds  to  unfold,  in  jars  containing  various 
gases.  In  hydrogen  or  nitrogen  the  twigs  decayed,  but  in  the  air 


Fig.  8. — .Experiment  to  ascertain  the  effect  of  gases 
on  the  roots  of  plants. 

the  buds  opened  and,  on  analysis  of  the  air,  oxygen  was  found 
to  have  disappeared.  It  thus  became  evident  that  the  buds  require 
oxygen  for  their  development. 

In  similar  experiments  with  flowers,  De  Saussure  found  that 
they  consume  several  times  their  volume  of  oxygen  in  24  hours. 
De  Saussure2  tested  the  effect  of  different  gases  upon  roots  of 

1  Johnson,  How  Crops  Feed,  p.  23. 

2  Johnson,  How  Crops  Feed,  p.  24. 


44  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

plants  by  cementing  the  plant  in  a  bell  jar,  so  that  the  stem  and 
leaves  were  in  the  outer  air,  while  the  roots  were  within  the 
vessel  and  exposed  to  any  gases  that  might  be  placed  therein. 
The  horse  chestnut  died  in  7  to  8  days  when  its  roots  were  placed 
in  carbonic  acid  gas,  in  from  13  to  14  days  in  nitrogen,  or  hydro- 
gen, while  the  plant  remained  healthy  to  the  end  of  the  experi- 
ment (21  days)  when  the  roots  were  in  contact  with  air.  The 
experiment  shows  that  the  roots  of  this  plant  require  oxygen, 
though  it  lived  for  some  time  without  oxygen.  Other  experi- 
ments show  that  roots  absorb  oxygen  and  give  off  carbon  dioxide. 
The  roots  of  some  plants,  which  prefer  heavy,  wet  soils,  probably 
do  not  require  oxygen.  The  difference  in  the  root  requirements 
of  plants  for  oxygen  is  probably  one  factor  in  their  adaptation  to 
various  types  of  soil. 

Nitrogen. — The  nitrogen  of  the  air,  which  makes  up  four-fifths 
of  its  volume,  is  in  the  free  state,  and  enters  into  combination 
only  with  difficulty.  So  far  as  animals  and  the  majority  of  plants 
are  concerned,  the  nitrogen  of  the  air  serves  only  as  a  dilutant 
for  the  oxygen,  which  would  have  too  energetic  an  oxidizing 
action  if  in  the  pure  state. 

To  be  of  value  to  animals  or  to  most  cultivated  plants,  nitrogen 
must  be  in  combination.  This  store  of  combined  nitrogen  is  com- 
paratively small.  Plants  and  the  bodies  of  animals  contain  some 
combined  nitrogen ;  there  is  some  in  the  soil,  coal  contains  a  small 
percentage,  and  there  are  some  deposits  of  nitrate  of  soda. 
Combined  nitrogen  is  lost  when  organic  matter  is  burned,  any 
nitrogen  present  being  evolved  in  the  free  state.  Explosives  are 
rich  in  nitrogen,  which  is  set  free  when  they  are  used.  In  certain 
processes  of  decay,  free  nitrogen  is  evolved. 

The  supply  of  combined  nitrogen  in  the  soil  is  comparatively 
small,  and  it  is  constantly  drawn  upon  by  crops.  Under  our 
present  system  of  agriculture,  the  stores  of  nitrogen  in  the  soil 
are  exploited  and  depleted.  A  considerable  quantity  of  nitrogen 
is  washed  from  the  soil  by  water.  Maintaining  the  fertility  of 
the  soil  is  largely  a  question  of  maintaining  its  store  of  combined 
nitrogen.  Fortunately,  we  have  now  obtained  the  means  for 


THE  PLANT  AND  THE  ATMOSPHERE  45 

causing  the  free  nitrogen  of  the  air  to  enter  into  combination. 
The  ways  at  present  in  which  this  is  accomplished  are  as 
follows : — 

1 i )  One  process  is  the  assimilation  of  free  nitrogen  by  bacteria 
in  symbiosis  with  leguminous  plants.     This  method  is  the  most 
promising  for  practical  agriculture.     The  energy  of  the  sun  is 
utilized  and  the  nitrogen  is  converted  directly  into  organic  matter. 
Some  bacteria  appear  to  be  able  to  assimilate  nitrogen  without  the 
aid  of  plants. 

(2)  Another      process      is      the      electrical      production      of 
nitric    acid    or    nitrates.      An    electrical    discharge    is    passed 
through      air      or      through      a     mixture      of      nitrogen      and 
oxygen,    and    the    oxides    of    nitrogen    produced    thereby    are 
absorbed  by  water  or  sodium  carbonate  or  caustic  soda.     When 
water  is  the  absorbing  medium,  nitric  acid  is  produced ;  if  caustic 
soda  or  lime  is  used,  nitrates  are  produced,  which  may  be  used 
as  a  fertilizer.     Since  nitric  acid  is  more  valuable  than  nitrate  of 
soda,   nitric   acid   is   made   when   practicable.     This   method   is 
practicable  only  when  electricity  can  be  produced  cheaply,  such 
as  is  accomplished  by  water  power. 

(3)  Production    of    Calcium    Cyanamid.1     Air,    freed    from 
oxygen  by  passing  over  heated  metallic  copper,  is  passed  into  a 
mixture  of  calcium  carbonate  and  carbon  heated  in  the  electric 
furnace.     The  first  product  is  probably  calcium  carbide: — 

2CaCO3  +  50  =  2CaC,  +  3CO2. 

This  is  then  converted  by  absorption  of  nitrogen  into  calcium 
cyanamid : 

CaC2  +  2N  =  CaCN2  +  C. 

The  product  contains  15  to  25  per  cent,  nitrogen  and  is  used 
directly  as  a  fertilizer.  A  cheap  source  of  electrical  energy  is 
required. 

Circulation  of  Nitrogen. — The  circulation  of  nitrogen  is  some- 
what more  complicated  than  that  of  carbon.     The  diagram  shows 
the  various  processes  which  it  undergoes. 
1  Bulletin  63,  Bureau  of  Soils. 


46  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Argon,  which  is  found  in  the  air,  is  a  gas  related  to  nitrogen 
and  is  apparently  incapable  of  entering  into  chemical  combination. 
It  has  no  agricultural  importance.  Associated  with  argon  in  the 
air,  in  very  small  quantity,  are  the  other  gases  of  similar  char- 
acter, namely,  neon,  helium,  krypton,  and  zenon. 


A  TMO 5PHE7VC  NITROGEN 


Fig.  9.— Circulation  of  nitrogen. 

Ammonia. — The  air  contains  about  one  part  of  ammonia  in 
fifty  million.  The  column  of  air  resting  on  an  acre  weighs  about 
41,300  tons,  which  would  contain  about  1.5  pounds  ammonia. 
Country  air  contains  less  ammonia  than  town  air.  The  ammonia 
in  the  air  probably  comes  from  the  decay  of  organic  nitrogenous 
bodies,  especially  urine.  The  exhalations  of  volcanoes  and 


THE  PLANT  AND  THE  ATMOSPHERE  47 

fumeroles  also  contain  ammonia,  which  may  be  due  to  the  action 
of  water  on  nitrides. 

Ammonia  gas  is  absorbed  by  the  foliage  of  plants,  as  has  been 
shown  by  experiments  such  as  the  following  of  Peters  and  Sachs.1 
The  stem  of  a  bean  plant  was  cemented  under  a  bell  jar.  The 
leaves  and  foliage  were  within  the  jar,  while  the  roots  and  soil 
were  outside.  The  plant  was  supplied  through  tubes  with  air 
mixed  with  4-5  per  cent,  carbon  dioxide.  Another  plant  in  a 
similar  apparatus  was  supplied  with  the  same  gases,  but  they 
were  passed  through  a  dilute  solution  of  carbonate  of  ammonia, 
which  gives  off  ammonia.  After  two  months,  the  plant  supplied 
with  ammonia  weighed,  when  dried  thoroughly,  6.74  grams,  and 
contained  0.208  gram  nitrogen;  the  other  plant  weighed  4.14 
grams,  and  contained  0.106  gram  nitrogen.  The  gain  of  nitrogen 
must  have  been  caused  by  the  absorption  of  ammonia  by  the 
foliage  of  the  plant.  If  the  entire  plant  and  the  soil  in  which  it 
grew  had  been  placed  in  the  bell  jar,  ammonia  would  have  been 
absorbed  by  the  soil  and  presented  to  the  roots.  But  the  arrange- 
ment of  the  experiment  eliminated  this  possibility,  since  the  soil 
and  roots  did  not  come  in  contact  with  the  ammonia  at  all. 

The  ammonia  of  the  atmosphere  is  in  such  small  quantity  that 
it  has  practically  no  effect  upon  plants.  This  has  been  shown  by 
experiments  such  as  the  following:  Hellriegel2  grew  lupines  in 
sterilized  sand  supplied  with  all  plant  food  except  nitrogen.  The 
nitrogen  content  of  both  seed  and  sand  had  been  previously  ascer- 
tained by  analysis.  After  the  plants  had  reached  their  full 
development,  both  plants  and  soil  were  subjected  to  analysis,  and 
the  amount  of  nitrogen  found  was  .007  gram  less  than  was  present 
in  the  seeds  planted  and  in  the  original  soil.  The  plants,  there- 
fore, had  lost  a  small  amount  of  nitrogen,  instead  of  gaining  any 
from  the  free  nitrogen,  or  from  the  ammonia  of  the  air. 

Nitric  Acid. — Nitric  acid  occurs  in  the  air,  probably  in  com- 
bination with  ammonia.  It  is  formed  by  electrical  discharges 
(lightning).  The  quantity  of  nitric  acid  in  the  air  is  very  small, 

1  Johnson,  How  Crops  Feed,  p.  56. 
-  Exp.  Sta.  Record,  5,  844. 


48 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


however,  and  the  plants  are  unable  to  absorb  any  appreciable 
quantity  directly  from  the  atmosphere. 

Combined  Nitrogen  in  Rain  Water. — The  atmospheric  ammonia 
and  nitric  acid  are  chiefly  of  importance  from  the  fact  that  they 
are  brought  to  the  soil  in  rain,  dew  or  snow,  and  thereby  afford 
nourishment  for  plants. 

The  quantity  of  combined  nitrogen  in  the  rain  has  been  ascer- 
tained at  a  number  of  Experiment  Stations,1  by  determining  the 
quantity  and  composition  of  each  rainfall.  The  results  of  a 
number  of  series  of  observations,  each  extending  over  a  period  of 
a  year  or  longer,  are  summarized  in  the  following  table : 

COMBINED  NITROGEN  IN  RAINFAU,  PER  YEAR  IN  POUNDS  PER  ACRE. 


(a) 

Nitrogen 
as  ammonia 

(b) 

Nitrogen  as 
nitric  acid 

(a  +  b) 
Total 
combined 
nitrogen 

Temperate  Zone  — 

5-72 
12  95 
0.50 

3-38 
2-95 
2.62 

4.26 
14.05 

I-I3 

2.27 
6.97 

I.I3 

0.24 

I.I3 
1.04 

3-33 

6.24 
0-75 

7-99 
19-93 
1.63 
3.62 
4.08 
3-66 

7-59 
19-25 

1.88 

Minimum  (  Ploty  )  

Rothauisted    lintjlaiid  

Kansas    

Tropical  Zone  — 

There  appears  to  be  considerable  variation  in  the  quantity  of 
combined  nitrogen  brought  to  the  earth  by  the  rain;  the  average 
for  the  temperate  zone  is  8  pounds  per  acre.  This  is  sufficient 
to  produce  approximately  5.3  bushels  of  corn,  leaves  and  stalk 
included.  But  it  is  probable  that  the  water  which  percolates 
through  the  soil,  in  humid  regions,  takes  out  more  combined 
nitrogen  than  is  brought  down  by  the  rain. 

Hydrogen  Peroxide. — Country  and  sea  air  contains  a  small 
quantity  of  a  powerful  oxidizing  agent,  which,  according  to 
1  Miller,  Jour.  Agr.  Sci.,  1905,  p.  280. 


THE  PLANT  AND  THE  ATMOSPHERE  49 

Schone,1  is  hydrogen  peroxide,  though  it  is  often  said  to  be  ozone. 
This  substance  is  destroyed  by  putrescible  substances,  and  it 
destroys  bacteria.  The  presence  of  hydrogen  peroxide  is  thus 
evidence  of  the  purity  of  the  air  as  regards  freedom  from  bacteria 
and  putrescible  bodies.  Hydrogen  peroxide  does  not  occur  in 
the  air  of  towns  or  marshes,  since  any  formed  is  instantly 
destroyed  by  the  organic  matter  present. 

At  Montsouris,  near  Paris,  the  amount  of  hydrogen  peroxide 
in  the  air  was  estimated  to  be  on,  an  average,  about  one  part  in 
100,000,000  for  a  period  covering  thirteen  years. 

Hydrogen  peroxide  may  be  formed  by  electrical  discharge 
(lightning)  and  in  some  processes  of  oxidation.  It  acts  upon 
iodide  of  potassium,  liberating  iodine,  which  turns  starch  blue. 
Paper  impregnated  with  potassium  iodide  and  starch  is  a  delicate 
test  for  ozone,  or  hydrogen  peroxide,  since  very  small  quantities 
of  these  substances  suffice  to  turn  it  blue. 

Other  Constituents  of  the  Air. — Marsh  gas  (CH4)  is  a  colorless 
and  odorless  gas  produced  in  the  decay  of  vegetable  matter  under 
water,  as  in  marshes,  and  in  the  digestion  of  hay  and  other  food 
by  herbivorous  animals.  Small  quantities  of  it  occur  in  the  air. 

Sulphur  dioxide  may  occur  in  the  air  in  the  neighborhood  of 
smelters,  factories,  or  in  towns.  If  present  in  appreciable  quan- 
tity, it  is  injurious  to  vegetation.  It  is  evolved  from  the  oxida- 
tion of  sulphur  during  the  combustion  of  coal. 

Dust  particles,  organic  matter,  and  salts  from  the  evaporation 
of  the  spray  of  the  sea,  are  found  in  the  air. 

Bacteria  are  also  present,  in  much  greater  numbers  in  the  city 
than  in  the  country.  Levy  found  345  per  cubic  meter  in  the  air 
of  Montsouris,  4,790  in  the  air  of  Paris  (average  of  13  years). 

Composition  of  Rain  Water. — Rain  water  has  been  converted 
into  vapor  by  the  sun,  and  condensed  again  into  a  liquid.  In 
its  passage  through  the  air,  rain  water  takes  up  ammonia,  nitrates 
dust,  chlorides  and  other  constituents  of  the  air.  Rain  water, 
therefore,  though  it  is  the  purest  natural  water,  is  not  absolutely 
pure. 

1  Berichte,  1880,  p.  1503. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


In  exceptional  cases  it  has  been  known  to  contain  so  much  dust 
as  to  assume  a  red  or  black  color.  It  usually  contains  a  small 
amount  of  chloride  of  sodium,  and  sulphates.  The  following  is 
a  summary  of  a  large  number  of  analyses  of  rain  water  made  by 
Angus  Smith.1 

ANALYSES  OF  RAIN  WATER— PARTS  PER  MILLION. 


Chlorides 
(as  sodium 
chloride) 

Sulphates 
(as  sodium 
sulphates) 

Ammonia 

Nitric  acid 

Scotland— 
Five  coast  country  places   •  . 
Twelve  inland  country  places 

20.3 

5-6 

9-7 
14.4 

6.4 
3-5 
19.2 
60.7 

0.48 

0-53 

3-82 

4-99 

0-37 
0.31 

i.z6 

0.85 

We  find  from  the  table  that  the  coast  rain  water  contains  more 
salt  (sodium  chloride)  than  the  rain  of  inland  places.  This  is 
due  to  the  salt  spray  from  the  sea,  which  is  broken  up  into  fine 
particles,  and  carried  by  air  currents  for  long  distances.  The 
effect  of  the  sea  upon  rain  water  is  often  noticeable  for  a  hun- 
dred miles  inland. 

Comparing  rain  water  of  the  city  and  of  the  country,  we  find 
that  the  former  is  marked  by  the  presence  of  considerably  more 
sulphates  and  ammonia,  and  that  it  also  contains  free  acid.  The 
increased  quantity  of  sulphates  and  the  sulphuric  acid  in  the 
rain  water  of  cities  can  be  traced  to  the  combustion  of  coal  con- 
taining sulphur. 

Arid  and  Humid  Climates. — In  a  humid  climate,  the  rainfall  is 
sufficient,  or  more  than  sufficient,  for  the  production  of  culti- 
vated crops.  In  an  arid  climate  the  rainfall  is  insufficient  in 
quantity,  and  crops  can  be  grown  only  through  irrigation,  or 
by  means  of  special  methods  of  culture.  The  character  of  the 
rainfall  also  influences  the  relation  of  the  climate  towards  crops. 
A  comparatively  small  amount  of  rain  distributed  through  the 
growing  season  may  give  a  locality  the  characteristics  of  a  humid 
region,  while  a  heavier  rainfall  so  distributed  that  very  wet 
periods  are  followed  by  long  intervals  of  little  or  no  precipita- 
1  Jour.  Chem.  Soc.,  1872,  p.  33. 


THE  PI.ANT  AND  THE  ATMOSPHERE  51 

tion,  may  give  an  arid  or  semi-arid  climate.  When  the  average 
annual  rainfall  is  20  inches  or  below,  it  is  generally  assumed  that 
crops  cannot  be  grown  without  irrigation. 

Soil  Atmosphere. — The  gases  which  occupy  the  pores  of  soils 
differ  in  composition  from  the  atmosphere,  chiefly  in  the  fact  that 
they  contain  much  more  carbon  dioxide  and  less  oxygen. 

The  oxygen  of  the  soil  atmosphere  performs  the  following 
functions : 

(1)  It  oxidizes  the  organic  matter,  producing  carbon  dioxide. 
Bacteria  play  an  important  role  in  this  change.     In  the  absence 
of  air,  putrefaction  takes  place,  with  production  of  acid  or  bad 
smelling  bodies. 

(2)  It  is  necessary  for  the  oxidation  of  organic  nitrogen  or 
ammonia  to  nitrates. 

(3)  It  is  necessary  for  the  roots. 

(4)  It  oxidizes  partly  oxidized  mineral  compounds,  such  as 
ferrous  or  manganous  salts. 

The  nitrogen  of  the  soil  atmosphere  is  fixed  by  legumes,  in 
co-operation  with  certain  bacteria,  producing  organic  nitrogenous 
compounds. 

The  carbon  dioxide  of  the  soil  atmosphere  is  formed  by  pro- 
cesses of  oxidation,  and  it  is  also  evolved  by  the  roots  of  plants. 
If  not  removed  with  sufficient  rapidity,  it  excludes  oxygen,  and 
thereby  interferes  with  the  normal  processes  of  the  soil.  The 
carbon  dioxide  of  the  soil  increases  the  solvent  action  of  the  soil 
water,  thereby  aiding  in  the  disintegration  of  the  minerals  of 
which  the  soil  is  composed,  and  in  the  solution  of  plant  food. 

Processes  of  Soil  Ventilation. — The  exchange  of  gases  between 
the  atmosphere  and  the  soil  atmosphere  depends  to  a  consid- 
erable extent  upon  the  character  of  the  soil.  A  coarse-grained, 
open  soil  is  much  more  easily  ventilated  than  heavy,  stiff  soils. 
Indeed,  it  is  possible  that  processes  of  oxidation  take  place  too 
rapidly  in  some  porous  soils,  resulting  in  the  rapid  loss  of  nitro- 
genous material  and  consequent  poverty  of  the  soil. 

The  particles  of  air  in  the  soil  tend  to  move  out  into  the  atmos- 


52  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

phere,   and   those   without   move   in.     This   process,   known   as 
diffusion,  though  a  slow  process,  aids  in  soil  ventilation. 

Air  expands  when  its  temperature  is  raised,  and  contracts 
when  it  cools.  These  changes  also  aid  in  soil  ventilation.  So 
do  the  expansion  and  contraction  resulting  from  barometric 
changes.  Gusts  of  wind  exert  a  suctional  effect.  When  water  is 
removed  from  the  soil,  air  enters  in  its  place. 


CHAPTER  IV. 


ORIGIN  OF  SOILS. 

The  soil  is  the  solid  outer  covering  of  the  earth,  which,  by 
being  disintegrated  into  particles,  and  provided  with  organic 
matter  and  nitrogen,  has  become  capable  of  sustaining  the  growth 
of  cultivated  plants. 

The  chemical  composition  and  physical  character  of  the  soil 
are  closely  related  to  the  material  of  its  origin  and  its  mode  of 
formation. 

Geology  teaches  that  ages  ago  the  surface  of  the  earth  was  a 
mass  of  rock,  formed  by  the  solidification  of  molten  material. 
Since  then  mountain  chains  have  been  elevated  and  razed,  and 
succeeded  by  new  mountains  which  have  been  likewise  eroded  and 
succeeded  by  others.  Lakes  have  been  filled  up  or  drained, 
rivers  have  eroded  channels  and  deposited  sediment.  Land  now 
dry  has  been  deposited  under  water.  Great  changes  of  climate 
have  occurred.  During  one  period  the  vegetation  was  tropical  in 
character.  At  another  time,  the  climate  was  colder,  and 
immense  sheets  of  ice  covered  the  northern  part  of 
North  America.  Races  of  plants  and  animals  have  appeared 
and  disappeared.  The  agencies  of  the  air,  and  water, 
have  broken  up  rocks,  carried  the  particles  away,  and  laid 
them  down,  perhaps  to  be  formed  into  rock,  elevated  into  land, 
and  to  go  through  another  series  of  decomposition  and  rock 
formation.  This  process  has  occurred  over  and  over  again.  In 
this  way  a  variety  of  rocks  and  a  great  many  soils  have  been 
formed. 

Soils  Formed  from  Rocks. — Soils  are  formed  by  air,  water,  heat, 
cold,  and  plant  life,  which  are  termed  weathering  agencies,  acting 
upon  rocks.  The  term  rock  in  the  geological  sense,  means  any 
layer  of  the  earth's  crust,  whether  hard  or  soft.  Thus  loose 
sand  and  clay  are  rocks  to  the  geologist  as  truly  as  sandstone 
or  granite.  The  soil  chemist,  however,  does  not  consider  un- 
consolidated  surface  deposits  as  rocks.  A  deposit  formed  by 
wave  action,  and  afterwards  elevated  so  as  to  become  a  soil,  is 
not  considered  as  a  rock,  but  as  a  transported  soil. 


54  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Weathering  agencies  act  upon  consolidated  and  unconsolidated 
rocks  exposed  on  the  surface  of  the  earth,  reduce  the  size  of 
the  particles,  and  change  the  rocks  chemically  and  physically. 
The  rocks  are  changed  into  soil  capable  of  supporting  the  growth 
of  cultivated  plants. 

Broken  rocks,  however  finely  pulverized,  do  not  constitute 
soil.  Besides  the  mere  mechanical  breaking  of  the  rock,  two 
other  processes  take  part  in  the  conversion  of  rock  into  soil. 
First,  a  greater  or  less  quantity  of  organic  matter  and  combined 
nitrogen  are  stored  up.  This  process  begins  with  the  bare  rock. 
Bacteria  first  appear.  These  take  up  carbon  dioxide  and  nitrogen 
from  the  atmosphere  and  leave  organic  matter  and  nitrogen  when 
they  die.  Then  mosses  and  lichens  begin  to  appear.  They  also 
have  the  power  of  taking  nitrogen  from  the  air.  As  the  weather- 
ing agencies  deepen  the  soil,  the  variety  of  plants  increases,  but 
almost  always  some  of  the  species  are  present  which  have  the 
power  of  causing  atmospheric  nitrogen  to  enter  into  combination. 
The  residues  left  when  the  plants  die,  store  the  soil  with  organic 
matter  and  nitrogen.  A  small  amount  of  organic  matter  and 
nitrogen  are  contained  in  rocks.1 

The  second  change  in  the  conversion  of  rock  to  soil  is  due  to 
the  fact  that  plant  food  becomes  more  easily  taken  up  by  plants 
than  it  was  in  the  original  rock.  This  is  in  part  due  to  chemical 
changes,  and  in  part  to  the  action  of  the  organic  matter  which 
has  been  added,  but  perhaps  to  the  greatest  extent  to  the  work- 
ing over  of  the  plant  food  by  the  past  generation  of  plants. 

Weathering  Agencies. — Weathering  is  the  term  applied  to  the 
natural  decomposition  or  breaking*  up  of  rocks,  and  weathering 
agencies  are  the  agencies  which  do  this  work.  Weathering  and 
weathering  agencies  are  studied  by  observing  the  changes  which 
are  now  going  on,  and  by  comparing  altered  rocks  with  the 
original  masses  from  which  they  were  derived. 

Weathering  processes  are  both  mechanical  and  chemical.  They 
are  mutually  helpful.  Mechanical  processes  reduce  the  size  of 
the  rock  fragments,  thereby  affording  more  surface  for  chemical 
1  Hall  and  Miller,  Jour.  Agr.  Sci.,  2,  p.  343. 


ORIGIN  OF  SOILS 


55 


action.  Chemical  processes  often  disintegrate  the  rock  into  very 
fine  particles. 

Changes  of  temperature,  moving  water,  and  ice,  act  mechanic- 
ally. The  chemical  agencies  are  chiefly  water  and  air.  Plant 
and  animal  life  act  both  mechanically  and  chemically. 

Changes  of  Temperature. — Changes  of  temperature  act  in  sev- 
eral ways. 

(i)  Molten  rock  masses  contract  on  cooling  and  become  per- 
meated by  fissures,  cracks,  and  joints. 


Fig.  10. — Rock  split  by  heat  and  cold. 

(2)  Water  enters  into  the  cracks  between  rock  masses,  and,  to 
some  extent,  into  the  pores  of  the  rock.  When  this  water  freezes, 
it  expands  one-fifteenth  of  its  bulk  and  exerts  a  tremendous  force. 
It  thus  splits  up  rock  masses,  and  disintegrates  rocks  which  are 
porous. 

(3)  Rocks  are  usually  composed  of   two  or  more  minerals, 
which   expand   differently   under   the   influence   of   heat.     Heat 
causes  the  different  minerals  to  expand  and  to  press  on  one  an- 
other, and  cold  makes  them  contract  and  move  apart.     In  time 
these  movements  so  impair  the  coherence  of  the  particles  as  to 
cause  gradual  disintegration  of  the  rock. 

(4)  Large  pieces  have  been  observed  to  split  off  from  bare 
rocks    exposed   to   the   sun.     This    is    due   to   expansion   under 
the    influence    of    heat,    and    can    take    place    to    any    extent 
only  on  mountain  sides  where  the  fragments  fall  away  from  the 
rock  surface. 


5«  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Moving  Water  and  Ice. — Water,  moving  from  higher  to  lower 
levels,  uses  the  rock  particles  it  carries  as  tools  to  scour  channels 
even  in  the  hardest  rocks.  The  sides  of  the  channel,  being  under- 
mined by  the  stream  and  loosened  by  frost,  fall  into  the  stream. 
The  rocks  grind  each  other  to  smaller  fragments.  All  of  this 
material  is  on  its  way  to  the  sea  or  to  a  lower  level  and  is  ground 
finer  as  it  is  carried  on. 

The  rate  of  movement  depends  upon  the  size  of  the  rock,  and 
the  size  and  velocity  of  the  stream.  A  portion  of  the  material 
is  deposited  by  the  stream,  perhaps  building  up  alluvial  soils,  but 
sooner  or  later  the  stream  will  begin  moving  it  towards  the  sea 


Fig.  n. — A  glacier  in  the  Alps. 

again.  Water-borne  materials  are  sorted,  that  is,  material  of 
nearly  the  same  size  is  deposited  together.  Layers  of  different 
material  may  alternate,  varying  with  the  velocity  of  the  water 
current. 

Rivers  of  ice,  or  glaciers,  are  formed  in  very  cold  climates,  or 
flow  from  the  sheets  of  perpetual  snow  covering  high  moun- 
tains. They  move  slowly,  grinding  rocks  together  with  enormous 
force,  and  form  deposits  different  in  character  from  those  of 
rivers.  The  fragments  are  more  angular  and  the  deposit  consists 


ORIGIN  OF  SOILS  57 

of  all  sizes  of  particles  together.  It  is  said  that  the  Rhone,  which 
is  fed  chiefly  from  the  glaciers  of  the  Alps,  carries  such  a  volume 
of  rock  dust  that  its  muddy  waters  may  be  traced  six  or  seven 
miles  after  they  have  entered  the  Mediterranean.  The  action  of 
glaciers  is  mechanical ;  the  rock  is  ground  up,  but  not  decomposed. 

Chemical  Action  of  Water  and  Air. — Water  acts  chemically 
upon  rock-minerals  by  solution  and  by  hydration.  Rain,  in  pass- 
ing through  the  air,  dissolves  oxygen,  carbon  dioxide,  and  other 
substances.  In  the  soil  the  water  absorbs  acids  formed  by  the 
decay  of  vegetable  matter.  These  substances  aid  in  its  weather- 
ing action. 

Hydration  is  a  chemical  change  in  which  the  mineral  combines 
with  water.  Some  minerals  take  up  water,  increase  in  bulk,  and 
fall  to  a  powder.  Hydrated  silicates  are  formed  from  various 
silicates. 

Solution. — There  are  very  few  minerals  which  do  not  give  up  a 
portion  of  their  constituents  to  water,  though  the  amount  of 
material  which  goes  into  solution  is  usually  very  small.  If 
pulverized  felspar,  amphibole,  etc.,  are  moistened  with  pure  water, 
the  latter  at  once  dissolves  a  trace  of  alkali  from  the  mineral,  as 
shown  by  its  turning  red  litmus  blue.  This  solvent  action  is  slight 
on  a  smooth  mass  of  the  material,  being  limited  by  the  extent  of 
surface.  Pulverization,  which  increases  the  surface,  increases 
the  solvent  effect  considerably. 

This  solution  involves  a  chemical  change,  new  bodies  with  new 
properties  being  formed.  Carbon  dioxide  and  oxygen  aid  the 
action  greatly.  For  example,  potash  felspar  is  decomposed  by 
water  with  the  formation  of  potassium  silicate  and  aluminium 
silicate.  In  the  presence  of  carbon  dioxide,  potassium  carbonate 
is  produced  and  hydrated  silica  set  free,  the  quantity  depending 
upon  the  amount  of  carbon  dioxide  present.  A  lime  felspar  is 
decomposed  in  the  same  way,  and  the  calcium  carbonate  dissolved 
by  aid  of  the  carbon  dioxide  the  water  contains.  Silicates  of  iron 
are  decomposed  with  the  production  of  hydrated  oxides  of  iron 
and  silicic  acid.  If  the  silicate  is  a  ferrous  silicate,  the  iron  is 
oxidized  by  the  oxygen  in  the  water. 
5 


58  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Carbonic  acid  increases  the  solvent  power  of  water.  Rain  water 
contains  from  5  to  10  parts  (by  volume)  of  carbon  dioxide.  River 
and  spring  waters  contain  more,  but  most  of  it  is  in  combination 
with  lime.  The  capillary  water  of  soils  containing  much  organic 
matter,  holds  more  carbonic  acid  in  solution  than  river  or  spring 
water. 

Water  containing  carbon  dioxide  is  especially  active  in  dissolv- 
ing carbonate  of  lime  or  limestone,  and  removing  it  from  the  soil 


Fig.  12. — Limestone  cavern. 

or  rock.     Carbonate  of  lime  is  slightly  soluble  in  water  (20  parts 
per  million),  but  much  more  soluble  in  water  containing  carbon 
dioxide,  owing  to  the  formation  of  calcium  bicarbonate : 
CaCO,  +  H,2O  =  Ca(HCO3)2. 

Water  saturated  with  carbon  dioxide  dissolves  about  880  parts 
per  million.  This  solvent  action  has  resulted  in  the  formation 
of  large  caverns  in  limestone  regions. 

Oxygen  is  also  dissolved  in  most  natural  waters,  and  acts  upon 
the  ferrous  or  manganous  compounds  which  occur  in  a  great 
number  of  minerals.  When  oxidized,  these  occupy  a  larger  space 
than  before,  and  thus  hasten  the  disintegration  of  the  minerals 
containing  them.  Some  ferrous  silicates  are  oxidized  rapidly  on 
exposure  to  moist  air,  falling  into  a  brown  powder  in  a  few  weeks. 


ORIGIN  OF  SOILS  59 

As  a  rule,  silicates  containing  much  iron  are  easily  changed  by 
weathering  agencies. 

Action  of  Animal  and  Vegetable  Life. — Animal  and  vegetable 
life  act  on  rocks,  both  by  their  living  activities  and  the  decay  of 
their  remains.  Vegetation  acts  both  mechanically  and  chemically 
upon  the  soil  and  rocks.  Roots  of  plants  penetrate  the  crevices 
of  rocks,  and,  as  they  grow,  split  even  large  rocks.  The  shelter 
of  growing  plants  keeps  the  rock  surface  moist,  thus  enabling  the 
water  to  act  upon  the  rock,  and  the  carbon  dioxide  excreted  from 
roots,  adds  its  effect  to  that  derived  from  other  sources.  Plants 
take  up  material,  which,  under  natural  conditions,  returns  to  the 
soil  in  a  modified  form. 

Earthworms  in  some  cases  bring  to  the  surface  large  quantities 
of  soil,  most  of  which  has  passed  through  their  intestines  and 
undergone  mechanical  and  chemical  changes. 

Vegetable  or  animal  residues  aid  weathering  in  several  ways : 

(a)  By  maintaining  more  moisture  in  the  surface  of  the  soil. 

(b)  By  supplying  copious  quantities  of  carbonic  acid.     The 
following  figures  of  Boussingault  and  Levy1  exhibit  the  amount 
of  carbonic  acid  in  the  air  of  the  soil  under  different  conditions : 

Carbonic  acid  in 
10,000  parts  by  weight 

Ordinary  air 6 

Air  in  sandy  subsoil  of  forest 38 

Air  in  loamy  subsoil  of  forest 124 

Air  in  surface  soil  of  forest 130 

Air  from  surface  soil  of  pasture 270 

Air  from  surface  soil  rich  in  humus 543 

Newly  manured  sandy  field  in  wet  weather 1413 

(c)  By  direct  action  of  organic  acids  such  as  acetic,  propionic, 
"humic,"  etc.,  which  are  found  in  vegetable  matter  or  produced 
in  its  decay. 

(d)  By   furnishing  a  medium   for  the  activity  of  the  lower 
soil  organisms,  such  as  bacteria  and  molds. 

Products  of  Weathering. — The  general  tendency  of  weathering 
is   towards   the   production   of   simpler   compounds    from   more 
complex  ones.     The  oldest  rocks  (which  are  igneous  in  origin) 
1  Jahresber.  der  Chem.,  1852,  p.  783. 


60  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

contain  complex  silicates  of  aluminium,  iron,  potassium,  sodium, 
lime,  etc.  The  tendency  of  weathering  is  to  reduce  these  to 
simple  compounds,  such  as  silica,  hydrated  oxides  of  iron, 
hydrated  silicates  of  aluminium,  carbonates  or  sulphates  of  lime 
and  magnesia,  chlorides  of  sodium  and  potassium,  and  sili- 
cates of  magnesia.  The  complex  silicates  are  not  changed  directly 
to  these  simple  bodies,  but  various  intermediate  products  are 
formed.  A  long  period  is  required  for  this  process  to  become 
complete,  so  that  in  many  soils  all  stages  of  the  change  may  be 
present,  from  particles  of  the  original  minerals,  through  various 
hydrated  silicates  derived  therefrom,  down  to  the  simpler  com- 
pounds. The  conditions  under  which  the  weathering  occurs 
determine  the  degree  of  decomposition.  If  the  weathering  agen- 
cies are  chiefly  mechanical,  the  rock  may  be  reduced  to  a  powder 
with  little  chemical  change. 

Loss  of  Material  by  Weathering. — In  every  case  of  weathering, 
a  greater  or  less  portion  of  the  constituents  of  the  rock  have  been 
carried  away.  An  estimate  of  the  loss  may  be  made  where  the 
soil  rests  directly  upon  the  rock  from  which  it  is  derived. 
Samples  of  the  soil,  and  of  the  unchanged  rock  beneath  it,  are 
subjected  to  analysis.  We  assume  one  ingredient  of  the  rock 
has  lost  nothing  in  weathering,  and  calculate  the  quantity  of  the 
original  rock  containing  the  amount  of  this  ingredient  found  in 
100  parts  of  the  soil.  This  gives  us  the  quantity  of  original  rock 
from  which  100  parts  of  soil  was  secured.  When  the  composition 
of  both  is  known,  it  is  a  simple  matter  to  calculate  the  loss  of  each 
ingredient. 

Suppose,  for  example,  the  original  rock  contained  30  per 
cent,  alumina,  and  the  weathered  product  contains  45  per  cent, 
alumina.  It  being  assumed  that  no  loss  of  alumina  took  place, 
150  pounds  of  the  original  rock  would  contain  45  pounds  of 
alumina;  that  is,  150  pounds  has  weathered  to  100  pounds.  If 
the  original  rock  contained  2  per  cent,  magnesia,  and  the  weath- 
ered product  0.5  per  cent.,  then  150  pounds  contained  three 
pounds,  and  we  have  0.5  pound  left,  giving  a  loss  of  five-sixths 
or  83^  per  cent,  of  magnesia.  Two  assumptions  are  made  in 
this  procedure ;  one  being  that  some  constituent  has  not  been  lost 


ORIGIN  OF  SOILS 


61 


at  all,  the  other  being  that  the  rock  from  which  the  soil  was 
derived  was  exactly  the  same  as  the  underlying  rock.  As  neither 
assumption  is  strictly  true,  the  method  gives  merely  approximate 
results. 

The  following  figures,  secured  by  the  method  outlined  above, 
are  compiled  from  Merrill's  "Rocks,  Rock  Weathering  and 
Soils." 

CALCULATED  PERCENTAGE  Loss  IN  WEATHERING. 


Granite 
Virginia 

Syenite 
Arkansas 

Limestone 
? 

Basalt 
Bohemia 

Soapstone 
Maryland 

Silica  (SiO  )  

52.5 
O 

14.4 

100.0 

74.7 

83.5 

95.0 

52.3 

0 

86.2 

57-9 
82.1 
81.9 
97.1 

O 
II.  4 

89.4 
66.3 

53-3 

33-i 

0 

50.2 

84.5 
74.1 
6i.7 

43-6 

0 

4i.5 
44.2. 
76.2 
47-1 

Alumina  (  A  1  O  )  

Ferric  oxide  (  Fe.2O8  )  
L/ime  (  CaO  )  •  •  •  •  •  

p0facVi  (  K  O^ 

coria  /Nfl  Q\ 

The  order  in  which  these  constituents  are  lost  varies  with  the 
rock  and  the  conditions ;  the  following  is  the  mean  order  in  seven 
cases : 

(i)  Lime,  (2)  potash,  (3)  magnesia,  (4)  soda,  (5)  iron, 
(6)  silica,  (7)  alumina.  That  is,  the  greatest  loss  is  usually  of 
lime,  the  next  greatest  is  potash,  and  so  on.  The  figures  given 
in  the  table  preceding  are  sufficient  to  show  the  profound  change 
which  may  occur  in  the  transformation  of  rock  into  soil  and  the 
large  amount  of  material  which  is  carried  away  during  weather- 
ing, probably  for  the  most  part  dissolved  in  water. 

Sedentary  and  Transported  Soils. — A  sedentary  soil  is  a  soil 
derived  from  the  weathering  of  a  rock  in  the  present  location  of 
the  soil.  On  making  an  excavation,  if  the  soil  is  sedentary,  we 
find  the  following :  First,  the  surface  soil ;  then  the  subsoil, 
lighter  in  color  but  of  the  same  general  character ;  and  at  a  lower 
depth,  we  find  the  subsoil  mixed  with  fragments  of  partly  weath- 
ered rock.  The  fragments  increase  in  quantity  until  finally  we 
come  to  the  solid  rock.  We  thus  observe  a  gradual  transition 
from  soil  to  rock,  and  therefore  infer  that  the  overlying  soil  is 
derived  from  the  decomposition  of  rock  which  formerly  occu- 


62 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


r// 


7/y 


ORIGIN  OF  SOII^S  63 

pied  its  position.  The  soils  derived  from  limestone  deposits  in 
Kentucky  and  in  Texas  are  sedentary,  and  so  are  the  soils 
derived  from  granite  and  other  igneous  rocks  which  are  common 
in  the  Piedmont  plateau  of  the  Atlantic  states.  Old  sedentary 
soils,  from  whatever  kind  of  rock  derived,  are  as  a  rule  clays 
colored  by  iron.  The  various  mineral  constituents  are  often  in 
an  advanced  stage  of  decay,  the  more  soluble  constituents  having 
been  largely  washed  out. 

A  section  of  the  soil  may  not  show  a  gradual  change  to  the 
underlying  rock,  but  the  change  may  be  abrupt  and  sudden. 
Such  a  soil  may  be  formed  when  the  soil  particles  are  brought 
from  other  localities,  and  deposited,  in  which  case  the  soil  is 
termed  a  transported  soil. 

Colluvial  and  Cumulose  Soil. — A  colluvial  soil  is  one  which 
has  been  removed,  to  some  extent,  from  the  original  position,  so 
as  to  mingle  with  other  rocks  and  layers,  as  when  a  soil  is 
washed  or  moved  down  hillsides  or  sloping  land.  Such  soils 
commonly  "creep"  or  have  a  slow  annual  movement.  Colluvial 
soil  particles  have  been  partly  moved  by  water,  but  have  not 
been  laid  down  under  water  as  have  alluvial  soils.  A  cumulose 
soil  has  been  formed  by  the  accumulation  of  vegetable  matter, 
such  as  occurs  in  swamps.  Peat  and  muck  are  cumulose. 

Soils  from  Igneous  Rocks. — Igneous  rocks  are  formed  by  the 
cooling  of  molten  matter  which  has  been  spread  out  upon  the 
surface  of  the  earth  or  injected  between  layers  of  other  rocks. 
Metamorphic  rocks  were  laid  down  by  water  or  other  agencies, 
but  were  afterwards  subjected  to  such  intense  heat  and  pressure 
as  to  crystallize  minerals  in  them. 

The  physical  and  chemical  character  of  the  rock  and  of  the 
soil  which  may  be  derived  from  it,  depends  upon  its  chemical 
composition,  and  the  rapidity  with  which  the  igneous  rock  solidi- 
fies. If  the  molten  mass  cools  off  rapidly,  so  that  it  solidifies  in 
a  comparatively  short  time,  minerals  do  not  have  time  to  crys- 
tallize, and  a  hard,  homogenous,  glassy  mass  is  produced  (glassy 
rock).  If  the  molten  material  remains  liquid  for  a  long  time 
and  cools  slowly,  the  rock  produced  is  a  mixture  of  definite 
minerals  which  can  be  easily  distinguished  (crystalline  rock). 


64 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Other  conditions  of  cooling  may  give  rise  to  a  compact,  stony 
mass,  composed  of  minute  crystals  (stony  rock)  or  to  a  rock 
containing  large  crystals  of  one  or  more  kinds  of  mineral  em- 
bedded in  a  stone  or  glass  matrix  (prophyry).  These  differences 


Fig.  14. — Microscopic  appearance  of  porphyry. 


Fig.  15.— Microscopic  appearance  of   granite. 

in  the  structure  of  rocks  of  the  same  composition  will  give  rise 
to  different  soils.  Glassy  rocks  will  produce  more  or  less  homo- 
genous particles,  while  crystalline  rocks  will  weather  into  par- 
ticles of  different  kinds,  perhaps  composed  of  the  different 
minerals. 


ORIGIN  OF  SOILS  65 

The  chemical  classification  of  igneous  rocks  depends  on  the 
relative  quantities  of  silica  and  bases  present.  Since  silica  is  the 
acid  portion  of  minerals,  rocks  containing  65  to  75  per  cent,  of 
silica  are  termed  acid  rocks,  those  containing  55  to  65  per  cent, 
are  called  intermediate,  and  those  carrying  40  to  55  per  cent,  are 
called  basic.  Crystalline  acid  rocks  contain  quartz,  while  basic 
rocks  do  not  contain  enough  silica  for  free  quartz  to  crystallize 
out. 

The  granite  group  comprises  rocks  rich  in  silica  and  alkalies, 
containing  65  to  75  per  cent,  silica  and  5  to  8  per  cent,  of  alkalies, 
of  which  y^  to  2/z  consists  of  potash.  They  are,  as  a  rule,  much 
richer  in  potash  than  other  igneous  rocks,  and  form  correspond- 
ingly better  soils. 

Granite,  the  crystalline  rock  of  this  group,  is  very  abundant, 
and  soils  derived  from  it  are  quite  common.  Granite  soils  are 
usually  clay  containing  particles  of  quartz  and  mica,  and  they  are 
often  fertile,  being  especially  rich  in  potash.  Rhyolite,  which 
is  a  porphyritic  rock  of  this  group,  is  extensively  distributed 
in  the  western  part  of  the  United  States. 

The  syenite  group  of  rocks  resembles  the  granite  group,  except 
that  the  rocks  contain  less  silica  (55  to  65  per  cent.)  and  more 
bases  to  correspond.  Like  the  granites,  the  syenites  are  rich  in 
potash. 

The  diorite  group  contains  about  the  same  amount  of  silica  as 
the  syenites,  but  less  alkalies  and  more  lime  and  magnesia. 

The  basalt  group  contains  the  basic  rocks  (40  to  55  per  cent, 
silica).  These  rocks  contain  small  amounts  of  alkalies,  and  are 
rich  in  iron,  lime,  and  magnesia. 

The  soils  of  the  Piedmont  plateau,  in  the  eastern  part  of  the 
United  States,  are  derived  mostly  from  igneous  or  metamorphic 
rocks,  and.  consist  of  sands  and  clays  containing  quartz  and  mica. 
This  area  extends  from  New  York  City  to  near  the  middle  of 
Alabama.  The  soils  of  the  eastern  Appalachian  Mountain  region 
are  also  of  similar  origin.  An  extensive  area  in  Washington, 
Oregon,  and  Montana  is  covered  with  soils  derived  from  the 
weathering  of  basalt  and  other  igneous  rocks. 


66 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Alluvial  Soils. — The  water  falling  on  the  ground  and  running 
off  on  its  surface,  carries  soil  particles  with  it.  Streams  or  rivers 
take  up  particles  of  rocks  or  soil  materials  and  carry  them  along. 
In  time  of  flood,  when  both  the  volume  and  velocity  of  the  stream 
are  increased,  this  burden  becomes  much  greater,  since  the  carry- 


CULF  or  vex/ co 


Fig.   16. — Sketch  map  showing  the  flood  plain  of  the  lower 
Mississippi.     U.  S.  D.  A. 

ing  power  of  water  increases  with  the  sixth  power  of  the 
velocity  with  which  it  moves.  That  is,  a  river  moving  at  the  rate 
of  four  miles  an  hour  may  carry  particles  sixty-four  times  as 


ORIGIN  OF  SOILS  67 

heavy  as  a  river  moving  at  the  rate  of  two  miles  an  hour.  While 
being  carried,  the  particles  are  ground  together  and  reduced  in 
size. 

Whenever  the  velocity  of  a  stream  is  decreased,  it  deposits  a 
portion  of  its  burden,  the  heavier  particles  being  deposited  first. 
Thus,  when  a  swollen  mountain  stream  issues  from  a  gorge  and 
spreads  out  over  a  plain,  it  deposits  a  portion  of  the  material  on 
the  surface  of  the  plain.  When  a  river  in  flood  leaves  its  banks, 
the  velocity  of  the  water  is  checked  on  spreading  over  the  plain, 
and  it  deposits  the  coarser  particles  which  it  carries  near  the 
channel  of  the  river.  The  finer  particles  are  carried  farther,  and 
are  deposited  in  the  swamps  or  low  ground  at  some  distance  from 
the  river.  The  tendency  of  a  river  bearing  rock  debris  is  to  build 
its  banks  up  above  the  level  of  the  surrounding  country.  The 
area  over  which  a  river  spreads  when  in  flood,  is  termed  its 
Hood  plain,  and  the  soil  formed  from  the  particles  which  it 
deposits  is  termed  an  alluvial  soil.  Some  of  the  richest  soils  in 
the  world  are  alluvial  soils.  The  soils  are  deep,  and  as  they 
receive  the  surface  soil  washed  away  from  less  fortunate  regions 
from  time  to  time,  their  fertility  is  maintained.  The  valleys  of 
the  Nile,  of  the  Ganges,  the  Mississippi,  the  Red  river,  the  Brazos, 
and  others,  contain  some  very  rich  soils,  which  are  alluvial  in 
origin.  The  soils  near  the  river  are  lighter  in  texture  than  those 
in  the  low  grounds  back  from  the  river.  The  latter  are  very 
heavy,  and  difficult  to  work,  but  are  often  very  productive. 

River  deposits  are  stratified;  that  is,  the  material  is  sorted  and 
deposited  in  layers  consisting  of  material  of  very  nearly  the  same 
fineness.  Layers  of  fine  and  coarse  material  may  alternate  accord- 
ing to  river  conditions. 

In  arid  regions,  where  the  streams  decrease  as  they  flow  from 
the  mountains  out  upon  the  dry  lowlands  and  are  therefore  com- 
pelled to  lay  aside  a  large  portion  of  their  burden,  mountain 
streams  may  form  wide-spread  alluvial  plains,  which  are  called 
piedmont  (meaning  foot  of  the  mountain)  alluvial  plains.  The 
streams  which  flow  eastward  from  the  Rocky  Mountains  have 
formed  a  continuous  alluvial  plain  which  stretches  hundreds  of 


68 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


miles  from  the  base  of  the  mountains,  the  deposits  being  in  places 
five  hundred  feet  thick.  These  deposits  are  now  being  eroded 
and  reworked  by  streams. 


Fig.  17.— Profile  showing  how  a  river  builds  up  its  banks 
near  the  channel.     U.  S.  D.  A. 

Alluvial  soils,  especially  if  deposited  by  large  rivers,  are  derived 
from  a  mixture  of  minerals  from  different  sources.  The  soils 
are  more  or  less  generalized  and  are  usually  very  productive. 
Alluvial  soils  are  found  near  rivers  in  all  sections  of  the  country. 
The  most  extensive  alluvial  soils  are  those  near  the  Mississippi 
River  and  its  tributaries,  especially  the  Red  River,  the  Arkansas, 
and  the  Missouri. 


Fig.  18. — Alluvial  cones,  Wyoming. 

Glacial  Soils. — A  glacier  is  a  river  of  ice.     It  carries  upon  its 
surface  and  within  its  mass,  soil  and  rock  fragments  derived  from 


ORIGIN  OF  SOILS 


6g 


the  hills  and  cliffs  which  it  passes.  This  material  consists  of  all 
grades  of  particles,  from  fine  fragments  to  large  pieces  of  rock. 
The  rock  fragments  are  usually  angular,  and  some  of  them  may 
be  marked  with  parallel  scratches.  These  scratches  are  caused  by 
a  rock  held  in  the  moving  ice  and  pressing  against  another  rock 
in  the  earth's  crust. 


Fig.  19.—  Unstratified  glacial  drift  near  Chicago. 

At  the  end  of  the  glacier  is  deposited  a  mixture  of  earth  and 
rocks  of  all  sizes,  which  is  known  as  a  moraine.-  When  the 
coming  of  a  higher  yearly  temperature  causes  the  front  of  a 
glacier  to  retreat,  it  leaves  the  surface  of  the  earth  covered  with 
the  mixed  deposit  characteristic  of  glaciers.  The  deposit  beneath 
the  glacier,  which  is  called  till,  is  sometimes  an  extremely  dense, 
stony  clay,  having  been  compacted  under  the  pressure  of  the 
moving  ice. 


7O  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  northern  part  of  the  United  States  was  once  covered  by  a 
great  glacier  sheet,  stretching  down  from  Canada.  Glacial  soils 
are  accordingly  found  in  New  York,  Ohio,  and  other  Northern 
States.  Some  of  these  deposits  have  been  reworked  by  rivers 
until  their  glacial  characteristics  are  no  longer  easily  recognized. 
Glacial  soils  are  especially  important  in  New  York  and  states 
north  of  it,  and  in  the  states  north  of  the  Ohio  and  Missouri 
rivers.  They  frequently  contain  considerable  amounts  of  car- 
bonate of  lime. 


Fig.  20.— Hypothetical  map  of  glacial  sheets  of  North 
America.     Salisbury. 

The  waters  from  the  melting  of  the  glacial  sheet  also  carried 
ground-up  material.  Though  this  was  sorted  by  the  water,  it  is 
different  from  ordinary  alluvial  soils.  These  soils  are  found  in 
the  area  adjacent  to  the  glacial  regions. 

Loess,  finely  ground  material  derived  from  glacial  drift  and 
transported  by  winds  or  flowing  water,  consists  of  grains  of 
quartz,  feldspar,  mica,  hornblende,  with  some  limestone  and  clay. 


ORIGIN  OF 

Wind  Blown  Soils. — In  any  region  where  the  soil  becomes  very 
dry  and  is  not  covered  with  vegetation,  as  in  deserts  or  arid 
sections,  the  soil  particles  may  be  taken  up  by  wind,  and  perhaps 
carried  considerable  distances.  The  attrition  of  the  wind-borne 
particles  reduces  the  softer  minerals  rapidly  to  dust,  and  harder 
minerals,  such  as  quartz,  more  slowly.  The  dust  and  sand  are 
separated,  as  the  dust  is  carried  farther.  Wind-borne  desert 
sands  thus  consist  largely  of  quartz.  Dust  carried  by  upward- 
whirling  winds  into  the  higher  currents  of  the  air,  is.  often  trans- 
ported for  hundreds  of  miles  beyond  the  arid  region  from  which 
it  is  taken.  In  1901  dust  carried  from  the  Sahara  northward  by 
a  storm,  fell  with  rain  over  southern  and  central  Europe  and  as 
far  north  as  central  Germany  and  Denmark,  causing  a  "black 
rain." 


Fig.  2i.— Dune  sands,  Lake  Michigan. 

In  northern  China  an  area  as  large  as  France  is  deeply  covered 
with  a  yellow  pulverulent  earth  called  loess,  but  which  many 
consider  a  dust  deposit  blown  from  the  great  Mongolian  desert 
to  the  west  of  it.  The  soils  of  some  of  our  western  States  are 
wind-blown  soils. 

Even  in  humid  climates,  in  many  places  along  the  seashore,  or 
lake  beaches,  as  in  New  Jersey  or  Michigan,  the  beach  sand  is 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


heaped  by  the  wind  into  wave-like  hills  called  dunes.  Dunes 
whose  sands  are  not  fixed  by  vegetation,  travel  slowly  with  the 
wind,  and  they  may  invade  and  destroy  forests  and  fields,  and 
bury  villages  beneath  their  slowly  advancing  waves.  River 
deposits  on  flood  plains  are  often  worked  over  by  the  winds  dur- 
ing summer  droughts,  and  much  of  the  silt  is  caught  and  held  by 
the  forests  and  grassy  fields  bordering  on  the  area. 

Wind-blown  materials  may  aid  in  the  formation  of  soils  even 
in  humid  regions.  Thus,  Hall1  relates  that  a  beach  composed  of 
coarse  rocks  (shingle)  was  found  in  years  to  have  accumulated 
a  few  inches  of  a  black  powder,  probably  borne  there  by  the 
wind. 

Soils  from  Oceanic  Deposits. — The  more  important  oceanic 
deposits  from  which  soils  are  derived  are  sands  and  sandstones, 


AfudandC/ays  Limestone  Sand 


Fig.  22. — Present  distribution  of  deposits  in  the  Atlantic  near 
the  United  States. 

muds,  shales,  and  other  consolidated   sediments,  and  limestone 
deposits.     The  material  of  the  oceanic  deposits  comes  from  the 
wear  and  tear  of  the  waves  on  the  shore,  and  from  the  waste 
1  The  Soil,  p.  10. 


ORIGIN  OF  SOILS  73 

brought  down  by  rivers.  It  is  estimated  that  the  waste  derived 
from  cliffs,  etc.,  along  the  seashore  is  about  three  per  cent,  of  that 
brought  down  by  rivers. 

Sands  are  deposited  along  the  shores  of  the  sea.  Boulders, 
pebbles,  and  coarse  sand,  are  deposited  in  order  near  in  shore,  and 
the  finer  sands  farther  out.  Beach  sand  derived  from  rocks  of 
neighboring  cliffs  or  brought  down  by  torrential  rains  from 
mountain  regions  is  dark,  and  contains  grains  of  many  minerals 
other  than  quartz.  These  sands  contain  more  plant  food  and 
make  richer  soils  than  sands  from  low-lying  shores.  The  white 
sand  of  low  shore  beaches,  such  as  those  on  the  east  coast  of  the 
United  States  from  Virginia  to  Florida,  consists  almost  entirely 
of  quartz  grains.  The  other  and  softer  minerals  have  been 
entirely  beaten  to  mud  and  deposited  farther  out  during  the  long 
period  that  the  material  has  been  exposed  to  the  waves.  These 
sands  are  poor  in  plant  food,  but  they  are  excellent  soils  for  some 
purposes. 

Sandstone  consists  of  sand  grains  cemented  together  by  silica, 
carbonate  of  lime,  or  oxide  of  iron.  Such  deposits  are  widely 
distributed,  and  many  soils  are  derived  from  them.  The  quality 
of  the  soil  depends  largely  upon  the  origin  of  the  sands.  Quartz 
is  sandstone,  which,  by  the  action  of  heat  and  pressure,  has  been 
metamorphosed  in  the  crust  of  the  earth. 

Muds  are  deposited  beyond  the  sand  deposits,  and  also  in  quiet 
water  near  shore,  and  in  river  deltas.  Muds  contain  the  finer 
particles  from  the  wear  of  rocks.  The  soils  derived  from  them 
contain  more  plant  food  than  sands  and  produce  longer,  but  are 
not  adapted  to  the  same  kinds  of  plants. 

Muds  may  be  consolidated  into  mudstone  or  shales  or 
metamorphosed  by  heat  and  pressure  into  schists  and  slates.  Soils 
are  formed  by  the  weathering  of  all  these  deposits. 

Limestone  deposits  are  formed  from  the  shells  of  molluscs,  and 
deposits  of  coral,  and  other  marine  organisms  which  secrete  car- 
bonate of  lime  from  solution  in  the  sea-water,  some  of  which  are 
minute  in  size.  These  deposits  are  usually  formed  in  the  shallow 
water  beyond  the  area  in  which  mud  is  deposited ;  they  also  make 
6 


74  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

up  a  large  part  of  the  deep  sea  deposit.     Phosphoric  acid  is  fixed 
in  small  quantities  in  these  deposits. 

Limestone  deposits  may  be  metamorphosed  into  limestone  rock, 
marble,  or  other  crystalline  forms  of  lime.  By  the  weathering  of 
such  deposits,  many  fertile  soils  have  been  farmed.  Some  old 
soils  of  limestone  origin  are  practically  free  of  carbonate  of  lime, 
and  are  very  poor. 

Deposits  in  Lakes. — Lakes  are  not  permanent,  geologically,  but 
are  gradually  filled  with  deposits  of  waste  brought  into  them  by 
rivers,  unless  the  lake  is  drained  before  such  filling  takes  place. 
The  lake  is  first  converted  into  a  swamp,  and  finally  into  dry  land. 

In  lakes  without  an  outlet,  various  salts  are  deposited.  Such 
lakes  can  exist  only  in  dry  climates,  where  the  loss  by  evaporation 
is  equal  to  or  greater  than  the  amount  of  water  brought  in  by 
rivers.  Rivers  carry  with  them  not  only  visible  waste,  consisting 
of  particles  of  rock  in  suspension,  but  also  invisible  waste,  or 
material  in  solution,  which  consists  of  carbonate  of  lime,  sulphate 
of  lime,  chloride  of  soda  or  common  salt,  etc.  This  waste 
accumulates  in  lakes  having  no  outlet.  Deposits  of  gypsum 
(sulphate  of  lime),  salt,  carbonate  of  lime,  and  other  salts,  are  left 
when  such  lakes  dry  up.  The  carbonate  of  lime  is  first  deposited, 
then  gypsum.  As  the  liquid  becomes  more  concentrated,  com- 
mon salt  is  deposited,  next  sulphate  of  magnesia,  then  potash 
salts,  and  chloride  of  magnesia.  The  deposition  may  be  checked 
by  influx  of  water  at  any  stage,  the  deposits  already  made  being 
perhaps  covered  with  mud,  and  a  new  series  of  deposits  started  on 
top  of  these.  The  German  potash  salts  are  supposed  to  be  of 
such  origin. 

Peat  and  Muck  Soils. — When  a  soil  is  saturated  with  water, 
vegetation  does  not  decay  as  rapidly  as  in  a  drained  soil,  but 
accumulates,  forming  a  peat  or  muck  soil.  Peat  soils  are  also 
formed  in  cool  and  damp  climates,  by  the  growth  of  a  moss, 
which  is  able  to  hold  water  tenaciously. 

Soil  Provinces  of  the  United  States. — The  Bureau  of  Soils1  of 
the  U.  S.  Department  of  Agriculture  divides  the  United  States 
1  Bulletin  No.  55. 


ORIGIN  OF  SOILS 


75 


into  thirteen  provinces,  based  chiefly  on  climate,  origin  and  topo- 
graphy of  the  soils.  These  are  better  shown  in  the  map  than 
described.  Two  great  divisions  are  based  on  climate ;  first,  humid, 
and  second,  arid  and  semi-arid.  The  soil  provinces  are  as  follows : 
Humid  Division. — i.  Atlantic  and  Gulf  Coastal  Plains. — These 
consist  of  a  belt  of  land  narrow  in  New  Jersey  but  much  wider 
towards  the  south.  The  surface  is  a  plain  cut  into  hills  and 
valleys  by  rivers,  about  200  to  300  feet  above  sea  level  along  the 
inner  margin,  but  nearer  the  coast  it  has  many  areas  with  deficient 
drainage.  The  soils  are  made  up  of  gravels,  sands,  and  sandy 
clays.  The  deposits  on  the  Atlantic  coast  are  derived  from  the 
Piedmont  Plateau  through  oceanic  agencies,  while  the  deposits  on 
the  gulf  coast  are  derived  from  material  transported  from  glacial 
deposits  and  from  the  western  plains.  There  are  also  some  soils 
derived  from  limestone  deposits. 


Fig.  23.— Shell  rock,  Florida. 

2.  Piedmont  Plateau. — This  area  lies  between  the  coastal  plain 
and  the  Appalachian  Mountains,  and  is  most  extensive  in  Virginia, 
North  Carolina,  South  Carolina,  and  Georgia.  The  altitude 
varies  from  300  to  over  1,000  feet  above  sea  level.  These  soils 
are  derived  largely  from  the  weathering  of  igneous  and 
metamorphic  rocks  in  place.  The  prevailing  series  of  these  soils 
are  the  Cecil  series  and  the  Chester  series.  Both  these  series 
usually  contain  mica  and  quartz. 


76  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

3.  Appalachian  Mountains  and  Allegheny  Plateau. — The  soils 
of   the   eastern   ranges   of   these  mountains   are   of    igneous   or 
metamorphic  origin,  while  the  western  ranges  and  the  Allegheny 
plateau    are   of    sedimentary    origin.     General    farming    is    not 
practiced  in  a  large  part  of  this  area  on  account  of  the  unevenness 
of  its  topography.     The  land  is,  however,  well  suited  to  grazing 
and  fruit  growing. 

4.  Limestone   Valleys  and  Uplands. — These  occur  in  narrow 
valleys  among  the  Appalachian  mountains  and  plateaus  near  by, 
and  in  two  large  areas,  one  in  central  Kentucky  and  Tennessee, 
the  other  in  Missouri  and  northern  Arkansas.     The  limestone 
soils  are  derived  from  the  weathering  of  limestone,  and  many  of 
them  contain  but  a  small  percentage  of  the  original  limestone 
rock.     Each  foot  of  the  soil  is  the  residue  from  the  weathering 
of  many  feet  of  the  rock. 

5.  Glacial  and  Loessial  Deposits. — This  area  covers  a  large 
portion   of   the   United    States,   especially   in   the   north-central 
states.     A  large  portion  of  this  area  was  covered  by  a  great  con- 
tinental glacier,  which  in  its  southern  movement  filled  up  valleys, 
plowed  off  hills   and  mountains,   and  deposited  the  ground-up 
material  varying  from  a  few  feet  to  over  30  feet  in  thickness. 
The   soils   are  partly  till,   or  heavy   clay  compacted  under  the 
glacier,  but  largely  "loess,"  a  fine  silty  deposit  containing  lime- 
stone and  very  fertile.     Some  of  the  material  was  brought  long 
distances,  but  most  of  it  is  composed  of  ground-up  underlying 
rock  largely  deposited  from  glacial  streams. 

6.  Glacial    Lake    and    River    Terraces. — These    are    deposits 
formed  by  the  Great  Lakes,  after  the  close  of  the  glacial  period, 
when  they  were  much  larger  than  they  are  now.  Several  terraces 
marked  by  the  old  shore  line  can  be  observed.  The  soils  vary  from 
beach   gravels   to    off-shore   deposits   of   heavy    clays,    and   the 
material  worked  over  by  the  water  is  partly  of  sedimentary  and 
partly  of  igneous  origin. 

7.  River  Flood  Plains. — These  soils  are  most  extensive  along 
the  Mississippi  and  its  tributaries,  and  along  rivers  in  Texas  and 
Louisiana,  though  soils  of  this  group  are  found  in  all  areas.  The 


ORIGIN  OF  SOILS 


77 


deposits  derived  from  various  kinds  of  materials  has  been  laid 
down  by  the  river  when  in  flood.  Such  soils  are  usually  fertile, 
though  they  may  not  always  be  profitably  cropped. 

Arid  and  Semi-Arid  Division. — 8.  Great  Basin. — The  soils  are 
derived  from  a  great  variety  of  rocks  and  consist  of  colluvial  soils 
of  the  mountain  slopes,  lake  and  shore  deposits,  stream  valley 
sediments,  and  river-delta  deposits. 

9.  Arid  Southwest. — These  soils  occupy  slopes  at  the  foot  of 
mountains,  alluvial  plains,  sloping  or  nearly  level  plains,  and 


Fig.  24.— Soil  provinces  of  the  United  States.     Bureau  of  Soils. 


stream  valleys.  The  soils  are  colluvial,  alluvial,  and  lake  deposits. 
Without  irrigation,  these  soils  have  little  agricultural  value. 

10.  Residual  Soils   of   the   Western  Prairie  Regions. — These 
soils  occupy  the  unglaciated  part  of  the  prairie  plains.     The  rocks 
from  which  the  soils  are  derived  are  of  the  carboniferious  age  and 
consist  of  sandstones,  shales,  and  limestones. 

11.  Northwestern  Inter-Mountain  Region. — The  soils  of  this 
area  consist  mostly  of  residual  material  derived  from  basaltic 


78  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

lava  and  in  some  cases  granitic  rocks.     Some  are  derived  from 
ancient  lake  beds. 

12.  Rocky    Mountain    Valleys,    Plateaus    and   Plains. — These 
soils  are  derived  from  a  great  variety  of  igneous,  metamorphic, 
and  sedimentary  rocks.     The  soils  of  the  mountain  slopes  are 
usually  of  little  agricultural  value,  while  those  of  the  plateaus, 
valleys,  and  plains  range  from  grazing  land  of  low  value  to  soils 
adapted  to  fruit,  sugar  beets,  and  other  special  crops. 

13.  Pacific    Coast. — Soils    found    in   this    region   range    from 
residual  and  colluvial  soils  of  the  mountain  sides,  foot  slopes  and 
foot  hills,  to  deep  and  extensive  river  flcod  plains  and  delta  sedi- 
ments, and  ancient  and  modern  shore  and  lake  deposits.     Their 
value  depends  largely  upon  possibilities  of  irrigation,  and  local 
conditions  of  rainfall  and  temperature. 


CHAPTER  V. 

PHYSICAL  COMPOSITION  AND  CLASSES  OF  SOILS. 

Soils  are  composed  of  particles  of  different  sizes,  ranging  from 
over  2  mm.  to  o.oooi  mm.  or  less,  in  diameter.  Many  of  the 
physical  properties  of  soils  are  closely  related  to  the  relative 
abundance  of  particles  of  different  sizes.  The  surface  area  of  a 
cubic  foot  of  the  particles  increases  with  their  fineness  of  division. 
The  retentive  power  for  moisture,  the  area  exposed  for  chemical 
action  and  for  the  feeding  of  roots,  the  capillary  action  of  the 
soil,  etc.,  are  closely  related  to  the  size  of  the  soil  particles. 

Soil  particles  may  be  found  independent  of  one  another,  but 
they  are  usually  more  or  less  united  into  crumbs,  compound 
particles,  or  lumps. 

Mechanical  Analysis. — By  the  mechanical  analysis  of  a  soil,  we 
mean  the  estimation  of  the  relative  quantities  of  soil  particles  of 
different  sizes.  As  the  particles  which  make  up  the  soil  have 
almost  an  infinite  variety  of  size,  all  that  can  be  done  is  to  group 
them,  by  placing  all  that  are  between  certain  dimensions  in  a  certain 
group.  The  sizes  selected  for  the  groups,  and  the  name  given  to 
each,  are  purely  arbitrary.  A  number  of  systems  of  soil  analysis 
is  possible.  The  principal  groupings  of  soil  particles  in  mechan- 
ical analysis  used  in  the  United  States  are  those  of  Hilgard,  and, 
those  of  the  Bureau  of  Soils.  Other  systems  are  used  abroad. 
The  Bureau  of  Soils  makes  seven  separations.  Dr.  E.  W.  Hilgard 
has  made  a  number  of  analyses  based  on  the  velocity  of  a  current 
of  water  holding  the  particles  in  suspension,  stated  in  millimeters 
per  second  (hydraulic  value).  For  example,  sand  of  0.5  to  0.30 
mm.  in  diameter  is  held  in  suspension  by  a  current  of  water 
moving  at  the  rate  of  64  millimeters  per  second. 

There  has  been  little  or  no  work  to  determine  the  classification 
of  soil  particles  which  would  best  correlate  the  properties  of  the 
soil  with  the  physical  analysis.  So  far  as  the  writer  has  been  able 
to  find,  the  division  into  groups  is  arbitrary. 

The  following  table  compares  the  systems  of  Hilgard  and  of  the 
Bureau  of  Soils : 


So 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Bureau  of  Soils 

Hilgard 

Name 

Sizes  of  particles 
MM. 

Sizes  of  particles 
MM. 

Hydraulic 
Value 

Name 

Stones,  sticks,  etc-- 

Over  2 

2-1 

1-0.5 
0.5-0.25 

0.25-0.1 

O.I-O.O5 
0.05-0.005 

3-i 
1-0.5 
0.5-0.3 
0.3-0.16 
O.J6-0.  1  2 
0.12-0.72 

O.O72-O.O47 
0.047-0.036 
0.036-0.025 
O.O25-O.OI6 
0.016-0.010 
0.010-    ? 

64 
32       }> 
16 

8     J 
4     1 

2 
I         }• 

05 
0.25  J 

Grit 
Sand 

Silt 
Clay 

Fine  suiid  

Silt  

Clav 

It  is  possible,  by  combining  some  of  the  groups  of  Hilgard,  to 
compare  the  results  with  analyses  of  the  Bureau  of  Soils.  As 
Hilgard1  remarks,  a  subdivision  of  six  or  seven  classes,  as  is 
made  by  the  Bureau  of  Soils,  is  sufficient  for  a  great  many  cases. 
There  is,  however,  considerable  difference  in  the  properties  of  the 
grades  of  silt  which  are  separated  by  Hilgard  but  grouped 
together  by  the  Bureau  of  Soils. 

Methods  of  Analysis. — For  the  separation  of  the  finer  particles, 
all  methods  of  mechanical  analysis  take  advantage  of  the  different 
rates  of  subsidence  of  particles  of  different  diameters  when  sus- 
pended in  water.  Methods  such  as  that  of  Osborne  depend  upon 
subsidence  under  the  influence  of  gravity  in  stationary  columns 
of  water.  Hilgard's  method  depends  upon  the  difference  between 
the  action  of  gravity  and  the  carrying  power  of  a  current  of 
water.  The  Bureau  of  Soils  throws  down  all  except  the  clay 
particles  by  centrifugal  force.  Sieves  are  used  for  separation  of 
the  coarser  particles ;  compound  particles  are  broken  down  by  shak- 
ing with  water,  or  boiling.  Since  clay  is  liable  to  form  compound 
particles,  and  otherwise  interfere  with  the  separations,  it  is 
removed  first. 
1  The  Soil. 


PHYSICAL  COMPOSITION  AND  CLASSES  OF  SOILS 


Si 


Method  of  the  Bureau  of  Soils.1 — The  following  is  an  outline 
of  the  method  of  mechanical  analysis  of  soils  used  by  the  Bureau 
of  Soils.  Five  grams  of  soil  are  shaken  for  six  hours  or  longer 


Fig.  25. — Centrifugal  machine  used  in  mechanical  analysis  of  soils. 

with  water  containing  a  little  ammonia,  in  order  to  decompose  the 
compound  particles.     The  soil  is  then  washed  into  a  centrifugal 
tube,  and  the  centrifugal  machine  run  at  full  speed  for  about 
1  Bulletin  24,  and  Bulletin  84. 


82  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

three  minutes,  the  time  depending  on  the  speed  of  the  machine 
and  the  quantity  of  suspended  material  present.  The  material 
in  suspension  is  then  examined  with  a  microscope  carrying  a 
micrometer  eye-piece,  to  see  if  any  particles  larger  than  clay  (.005 
mm.  in  diameter)  remain  in  suspension.  If  larger  particles  are 
found,  the  centrifugal  is  run  until  they  settle.  When  the  water 
contains  only  clay  particles,  it  is  decanted.  The  residue  is  stirred 
up  with  water,  the  machine  started,  and  the  separation  made  as 
before.  The  operation  is  repeated  until  the  clay  has  been  all 
removed,  as  shown  by  a  microscopic  examination  of  the  residue. 
The  water  is  evaporated  to  dryness,  and  the  clay  weighed. 

The  residue  left  in  the  tubes  is  brought  in  suspension  with 
water,  and  allowed  to  settle,  until  microscopic  examination  shows 
only  silt  in  suspension.  This  requires  but  a  short  time.  The  silt 
water  is  decanted,  and  the  operation  repeated  until  all  the  silt 
(less  than  .05  mm.  in  diameter)  has  been  washed  out.  The  silt, 
after  being  allowed  to  settle,  is  collected,  dried  and  weighed.  The 
sand  is  then  collected,  dried,  and  separated  into  five  groups  by 
means  of  a  nest  of  four  sieves,  two  of  brass  with  circular 
perforations  I  mm.  and  0.5  mm.  in  diameter,  and  two  of  silk 
bolting  cloth  with  openings  0.25  and  o.i  mm.  wide.  The  various 
separations  are  then  weighed. 

Hilgard's  Method. — The  following  is  an  outline  of  Hilgard's 
method.  (For  full  details  see  Wiley's  "Agricultural  Analysis.") 
The  two  grades  of  grit  are  removed  by  sieves.  Ten  or  15  grams 
of  the  sifted  soil  are  boiled  with  water  to  break  up  the  compound 
particles,  transferred  to  a  beaker,  mixed  with  water,  and  allowed 
to  stand  a  short  time  until  only  the  finest  silt  and  clay  remain 
in  suspension.  The  treatment  with  water  is  repeated  until  the 
water  has  removed  all  the  finest  silt  and  clay.  The  mixture 
of  clay  and  silt-water  is  allowed  to  stand  24  to  60  hours,  until  all 
silt  is  deposited.  The  sediment  is  rubbed  with  a  rubber  pestle, 
mixed  with  water,  and  allowed  to  settle  again  until  free  from 
clay.  It  is  then  dried  and  weighed.  An  aliquot  of  the  clay-water 
may  be  evaporated  to  dryness  and  the  residue  weighed,  or  the 
clay  may  be  precipitated  by  coagulation  with  salt. 


PHYSICAL  COMPOSITION  AND  CLASSES  OF  SOILS  83 

The  mixed  sediments,  containing  the  sand  and  all  the  silt 
except  the  finest,  is  placed  in  an  upright  glass  cylinder,  containing 
a  rotating  fan  or  churn,  run  by  a  suitable  motor.  This  breaks  up 
the  compound  particles.  A  current  of  water  is  run  in  so  that  it 
moves  through  the  cylinder  at  the  rate  of  0.25  mm.  per  second, 
until  the  water  becomes  clear.  The  particles  carried  over  are 
allowed  to  settle,  dried  and  weighed.  The  current  of  water  is 
increased  to  0.5  mm.  per  second,  so  as  to  remove  another  grade 


Fig.  26. — Hilgard's  apparatus  for  mechanical  analysis  by  means 
of  a  current  of  water. 

of  particles,  and  these  operations  are  repeated  until  all  the  grades 
of  particles  are  separated. 

Relation  of  Grain  Size  to  Soil  Texture. — This  relation  is  studied 
by  ascertaining  the  mechanical  analysis  of  soils  of  known  prop- 
erties, and  also  by  investigating  the  properties  of  the  various 
groups  of  particles  separated  in  the  analysis. 

In  sands  the  coarser  particles  of  the  soil  predominate.  Such 
soils  are  open  or  porous,  easy  to  cultivate,  not  very  retentive  of 
moisture,  and  warm  up  early  in  the  spring.  Coarse  sands  are 
least  retentive  of  moisture  and  most  porous.  Soils  containing 
quantities  of  very  fine  sand  are  much  more  retentive  of  moisture. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


In  heavy  clay  soils,  the  fine  clay  particles  are  present  in  large 
quantity.  Such  soils  are  very  retentive  of  moisture,  require 
much  labor  in  cultivation,  are  likely  to  be  tough  and  sticky  when 
not  ploughed  at  exactly  the  right  time,  are  not  easily  penetrated 


UNITED  STATES  DEPARTMENT  OF  AGRICULTURE, 


)l VISI..N    «>F    AGRICULTURAL    SO 


THE  TEXTURE  OF   A  TYPICAL    TOBACCO  LAND  AT  HATFIELD.  MASSA 


Par  Cent  of  Gravel.  Sand.  Silt,  and  Clav  in   2O  Cirams  of   Subsoil 


DIAMETER    OF   THE   GRAINS    IN    MILLIMETERS. 


Fig.  27. — Physical  analysis  of  a  soil  sample.     Bureau  of  Soils. 

by  water,  and  do  not  warm  up  rapidly  in  the  spring.     Twenty  per 
cent,  clay  particles  usually  make  a  soil  difficult  to  work. 

Soils  with  much  silt  and  little  or  no  clay,  are  likely  to  adhere 


PHYSICAL,  COMPOSITION  AND  CLASSES  OF  SOILS  85 

to  the  plow  very  tenaciously  when  too  wet.  They  plough  fairly 
well  when  in  right  condition,  but  turn  up  in  clods  if  ploughed 
when  dry.  Loams  are  intermediate  between  sands  and  clays,  in 
physical  character  and  in  properties,  and  in  general  are  good  soils. 

The  coarse  soil  particles,  therefore,  tend  to  make  the  soil  more 
open  and  porous  and  more  easily  tilled.  The  fine  particles  tend 
to  make  the  soil  more  compact  and  less  easily  tilled.  The  final 
resultant  depends  upon  the  relative  quantities  of  the  different 
kinds  of  particles,  as  well  as  their  chemical  composition  or  their 
properties.  The  presence  of  a  certain  amount  of  clay  in  a  sand 
is  desirable.  If  no  clay  is  present,  the  soil  is  liable  to  pack  on 
wetting,  but  clay  holds  the  particles  into  crumbs  characteristic  of 
a  well  tilled  soil.  Further,  sands  containing  less  than  4  per  cent, 
clay  have  little  power  of  retaining  moisture  and  are  particularly 
liable  to  suffer  from  drought  Sand  particles  in  a  clay  will  not 
diminish  its  stickiness,  while  silt  particles  make  the  clay  less 
adhesive,  though  perhaps  more  heavy  to  work. 

Mechanical  analysis  is  also  to  be  interpreted  with  consideration 
as  to  the  amount  and  distribution  of  rainfall  and  the  temperature 
and  the  effect  of  the  underground  water.  A  light  soil  under 
heavy  rainfall  may  behave  like  a  heavier  soil  under  light  rainfall. 
A  soil  with  ground-water  at  such  distance  that  it  may  be  brought 
to  the  roots  of  plants  by  capillary  action,  is  in  better  condition  than 
when  the  ground-water  is  deeper. 

Classes  of  Soil  Related  to  Mechanical  Analysis. — Soils  are 
classed  as  sands,  loams,  clays,  etc.,  according  to  their  physical 
characteristics.  There  is  room  for  difference  of  opinion  as  to 
exactly  what  characteristics  should  be  signified  by  each  term.  The 
classification  is  made  partly  by  field  observations,  and  partly  by 
mechanical  analysis. 

As  a  result  of  the  mechanical  analysis  of  a  great  number  of 
soils,  the  Bureau  of  Soils1  of  the  U.  S.  Department  of  Agriculture 
finds  different  types  to  have  the  following  average  composition 
(see  table). 

The  predominance  of  various  grades  of  material  is  well  brought 
out  in  the  table.  For  example,  the  coarse  sands  contain  on  an 

1  Bulletin  No.  78. 


86 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


average  31  per  cent,  coarse  sand  particles,  the  sands  37  per  cent, 
of  fine  sand  particles,  the  fine  sands  57  per  cent,  fine  sand 
particles.  The  clays  contain  42  per  cent,  clay  particles. 

AVERAGE  COMPOSITION  OF  SOIL  TYPES  AS  ANALYZED  IN  CONNECTION 
WITH  THE  SOIL  SURVEYS. 


Soil  classes 

Num- 
ber of 
sam- 
ples 

Fine 
gravel 

Coarse 
sand 

Med- 
ium 
sand 

Fine 
sand 

Very 
fine 
sand 

Silt 

Clay 

Coarse  sands  

flC 

Pet. 

Pet. 

Pet. 

Pet. 

Pet. 

Pet. 

Pet. 

Sands  

1OJ 

31 

J  V 

7 

5 

Fine  sands  

C  T  T 

Jo 

Z6 

37 

7 

Sandy  loams  

O1  A 

I   I  A.\ 

01 

A/ 

• 

Fine  sandy  loams  

934 

I 

Jo 

3 

4 

32 

16 

24 

24 

12 
T£ 

Silt  loams 

°oy 

T    2fi<S 

5 

•7 

4° 

162 

Q 

0 

5 

°5 

!5 

7l8 

3° 

T3 

-Q 

27 
if* 

7Ac- 

' 

M 

13 

3° 
fir 

Clav  .  . 

/UO 
I   Q7O 

Q 

Q 

T.ft 

*0 

J  >y/u 

3° 

4^ 

The  classification  of  soils  with  regard  to  physical  composition, 
as  used  by  the  Bureau  of  Soils,1  is  shown  in  the  following  table. 
The  classification  is  controlled  by  field  observations. 

CLASSIFICATION  OF  SOIL  MATERIALS. 
Soils  containing  — 20  silt  and  clay  : 

Coarse  sand  .    f  25-f  fine  gravel  and  coarse  sand, 

\       and  less  than  50  any  other  grade. 

can(j  I   25+  fine  gravel,  coarse  and  medium 

\      sand,  and  less  than  50  fine  sand. 

!5o-f  fine  sand,  or  — 25  fine  gravel, 
coarse  and  medium  sand,  50+ 
very  fine  sand. 

Very  fine  sand 50+  very  fine  sand. 

Soils  containing  20-50  silt  and  clay  : 

Sandy  loam .   /  25+ fine  gravel,  coarse  and  medium 

(      sand. 

Fine  sandy  loam |  50+  fine  sand,  or  -25  fine  gravel, 

(.       coarse  and  medium  sand. 

Sandy  clay 20  silt. 

Soils  containing  50+  silt  and  clay  : 

Loam 20  clay,  —50  silt. 

Silt  loam 20  clay,  50+  silt. 

Clay  loam 20-30  clay,  —50  silt. 

Silty  clay  loam 20-30  clay,  50+  silt. 

Clay 30-1-  clay. 

1  Bulletin  No.  78. 


PHYSICAL,  COMPOSITION  AND  CLASSES  OF  SOILS  S/ 

The  figures  given  represent  per  cent. ;  the  minus  sign  ( — )  repre- 
sents, less,  and  the  plus  sign  (-(-)  represents  more;  and  the  sign 
(-)  when  used  between  two  figures,  thus  20-50,  gives  limiting 
values,  and  should  be  read  from  20  per  cent,  to  50  per  cent.  Thus, 
25  +  means  25  per  cent,  or  more;  —  25  means  less  than  25  per 
cent. 

For  example,  a  soil  containing  less  than  20  per  cent,  silt  and 
clay  and  over  50  per  cent  fine  sand,  would  be  called  a  fine  sand. 
A  soil  containing  over  50  per  cent,  silt  and  clay  particles  and  over 
30  per  cent,  clay  would  be  called  a  clay  soil. 

Relation  of  Chemical  Composition  to  Soil  Texture. — The  effect 
of  the  physical  composition  of  a  soil  is  modified  by  the  chemical 
character  of  its  constituents.  The  three  important  modifying 
constituents  are  organic  matter,  colloidal  clay,  and  carbonate  of 
lime. 

Organic  matter  binds  a  loose  soil,  and  lightens  a  heavy  soil, 
and  thus  reduces  the  difference  between  them.  When  there  is  a 
large  quantity  of  organic  matter,  the  mechanical  analysis  loses 
much  of  its  significance. 

Carbonate  of  lime  (i  to  2  per  cent.)  also  lightens  a  clay  soil 
and  otherwise  modifies  its  properties.  For  example,1  the  follow- 
ing pairs  of  soils  had  similar  physical  composition  but  differed 
decidedly  in  properties : 


Per  cent,  carbonate  lime 

Holsey  green 

Rothamsted 

(  Q\  foo  sticky  to  be  cultivated  

0.48 
1.02 

0.16 

3-0 

(  \)\  Heavy  soil   but  works  well  

It  is  very  well  known  that  calcareous  clay  soils  are  more  easily 
cultivated  and  break  up  better  than  similar  soils  deficient  in  lime. 

The  clay  particles,  so  called,  may  be  composed  of  quartz  dust, 

hydrated   oxide   of    iron,   gelatinous    silica,    carbonate   of    lime. 

hydrated    silicates,    and    of    true   clay,    or   hydrated    silicate   of 

alumina.     These   substances   have   different  properties,   and   the 

1  Hall,  Jour.  Agr.  Sci.,  1911,  p.  187. 


88  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

composition  of  the  clay  particles  undoubtedly  influences  the  char- 
acter of  the  soil.  The  term  "Klay"  has  been  proposed  to  dis- 
tinguish the  clay  particles  of  a  soil  from  the  hydrated  aluminium 
silicate  termed  clay  by  the  chemist. 

True  clay  is  present  in  the  soil  in  two  forms.  First,  as  colloidal 
clay  in  a  swelled  condition;  and  second,  as  clay  in  non-colloid, 
or  shrunken  condition.  In  the  colloid  condition,  clay  remains 
suspended  in  water  indefinitely.  Small  amounts  of  lime  and  other 
substances  coagulate  the  clay  and  cause  it  to  separate  out  in  flakes. 
When  the  coagulating  substance  is  removed,  the  clay  again 
becomes  colloidal.  This  may  be  easily  shown  by  washing  a  clay 
soil  with  acid  to  remove  lime,  then  with  water,  and  shaking  it 
with  ammonia.  Clay  will  enter  into  suspension  and  remain  sus- 
pended a  long  time,  but  if  ammonium  sulphate,  ammonium  car- 
bonate, or  other  salts  are  added,  the  clay  quickly  separates  in 
flakes. 

Colloidal  clay  was  prepared  by  Schloesing.1  He  brought  the 
clay  into  suspension  in  water,  as  iri  the  mechanical  analysis  of  a 
soil,  and  precipitated  the  clay  with  a  small  quantity  of  acid, 
collected  the  colloidal  clay  on  a  filter,  and  washed  with  distilled 
water.  The  residue  on  the  filter  was  treated  with  ammonia,  and 
diffused  in  a  considerable  quantity  of  distilled  water.  This  was 
then  left  until  deposition  ceased,  which  required  several  months. 
The  microscope  could  then  no  longer  detect  particles  of  visible 
dimensions  in  the  solution.  The  liquid  was  decanted  off,  and  the 
colloidal  clay  precipitated  by  the  addition  of  a  small  quantity  of 
acid.  It  dried  to  a  translucent,  horn-like  mass.  According  to 
Schloesing,  even  the  stiffest  natural  clays  seldom  contain  more 
than  1.5  per  cent,  of  such  true  colloidal  clay. 

Colloidal  clay  has  much  higher  binding  properties  than  shrunken 
or  coagulated  clay.  The  tenacity  of  a  soil  containing  colloidal  clay 
is  greatly  influenced  by  its  condition.  If  the  clay  is  in  its  fully 
swelled  condition,  the  soil  exhibits  its  maximum  cohesion,  and  if 
a  sufficient  quantity  of  clay  is  present,  it  will  be  quite  impervious 
to  water.  If  the  colloidal  clay  is  in  a  shrunken  coagulated  state, 
1  Chimie  Agricole,  1885. 


PHYSICAL  COMPOSITION  AND  CLASSES  OF  SOILS  89 

the  same  soil  may  be  pervious  to  water  and  susceptible  of  success- 
ful tillage. 

Boiling  in  water,  freezing,  working  the  wet  soil,  alcohol,  ether, 
sodium  or  potassium  hydroxides,  ammonia,  and  sodium  or 
potassium  carbonates,  cause  the  clay  to  swell  and  increase  its 
colloidal  properties.  These  agencies,  therefore,  tend  to  make 
clay  soils  more  impervious,  sticky,  and  difficult  to  work.  Lime, 
magnesia,  bicarbonate  of  lime,  certain  acids,  such  as  hydrochloric 
or  sulphuric,  and  certain  salts  such  as  sodium  chloride,  sodium 
sulphate,  calcium  sulphate,  coagulate  the  clay  particles.  These 
substances,  therefore,  tend  to  make  clay  soils  less  sticky  and  more 
permeable  to  water. 

If  clay  is  washed  and  kneaded  when  wet,  it  becomes  plastic 
and  sticky,  and  may  be  moulded  into  forms  which  retain  their 
shape  and  become  hard  and  stony  when  dried  and  baked. 
Advantage  is  taken  of  this  property  in  the  manufacture  of  brick, 
earthenware,  and  chinaware,  but  it  is  not  a  desirable  property  in 
a  soil. 

Hydrated  oxide  of  iron,  and  some  of  the  other  bodies  which 
occur  in  the  clay  separation  do  not  have  the  binding  properties  of 
true  clay,  and  if  present  to  any  considerable  extent,  the  soil  may 
not  have  the  characteristics  which  would  be  expected  from  the 
quantity  of  clay  in  it.  Hilgard,1  for  example,  finds  that  a  certain 
clay  soil  containing  40  per  cent,  of  clay  was  scarcely  as  adhesive 
as  another  soil  containing  25  per  cent,  of  clay,  and  not  nearly  as 
sticky  when  wet  as  a  third  soil  containing  33  per  cent.  clay.  The 
soil  first  named,  however,  was  rich  in  ferric  hydrate,  a  large  por- 
tion of  which  is  probably  in  the  clay  particles.  This  accounts  for 
the  behavior  of  the  soil.  Ferric  oxide  appears  to  diminish  the 
tenacity  of  a  clay. 

Rivers  which  contain  little  lime  are  turbid  from  presence  of 
clay,  but  70  to  80  mg.  lime  per  liter  precipitates  the  clay  and  leaves 
the  water  clear. 

Calcareous  clays  are  very  sticky  when  wet,  but  many  of  them 
disintegrate  into  a  mass  of  crumbs  on  drying,  thereby  producing 
1  The  Soil,  p.  100. 
7 


9O  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

good  tilth,  even  though  worked  when  wet.  Non-calcareous  clays 
under  such  conditions  are  likely  to  contract  into  stony  masses.  The 
exact  proportions  of  carbonate  of  lime  necessary  to  produce  this 
condition  of  the  soil  remains  to  be  determined. 

The  black  prairie  soil  of  Texas  locally  called  "black  waxy"  and 
termed  the  "Houston  black  clay"  by  the  Bureau  of  Soils,  is  an 
example  of  this  kind  of  soil.  When  wet  it  is  gummy  and  waxy, 
but  when  dry  and  well  cultivated  it  is  friable  and  easily  worked. 
This  soil  contains  one  per  cent  or  more  of  lime.  Clay,  unlike  silt, 
chalk,  and  humus,  increases  greatly  in  coherence  when  it  dries, 
and  finally  becomes  a  hard,  solid  substance. 

Nature  of  Tilth.1 — If  the  particles  of  a  soil  are  each  inde- 
pendent of  the  other,  so  that  their  relative  positions  are  easily 
shifted  by  gravity  or  water,  they  are  said  to  possess  the  single- 
grain  structure.  Such  soils,  if  sandy,  are  loose,  and  become  as 
compact  as  their  particles  allow.  Clay  soils  of  this  character  are 
very  sticky  when  wet,  and  if  worked  while  wet  form  clods  on 
drying. 

A  soil  which,  when  plowed,  breaks  up  into  a  mass  of  compound 
particles  of  various  sizes,  loosely  piled  upon  one  another  and 
separated  by  comparatively  large  interspaces,  is  said  to  possess  the 
crumb  structure  and  to  be  in  good  tilth.  The  crumbs  may  be 
held  together  by  moisture,  clay,  humates,  carbonate  of  lime,  and 
sometimes  silica  and  oxide  of  iron. 

Crumbs  of  sand  held  together  by  water  collapse  on  drying. 
Clay  is  frequently  the  substance  which  holds  the  crumbs  together ; 
in  such  case,  the  crumb  structure  remains  even  after  the  land 
dries  out.  Beating  rains  and  cultivation  while  too  wet  destroy 
these  crumbs. 

Soil  particles  united  by  carbonate  of  lime,  humates,  silica,  or 
oxide  of  iron  are  more  or  less  permanently  cemented  into  com- 
pound particles.  In  some  calcareous  soils  we  find  sandy  and  silt 
concretions  varying  from  several  inches  in  size  to  microscopic 
proportions.  Humus  is  a  great  aid  in  securing  good  tilth. 

Compound  particles  are  also  formed  by  natural  processes,  due 
1  Warington,  Physical  Properties  of  Soil,  p.  36. 


PHYSICAL  COMPOSITION  AND  CLASSES  OF  SOILS  9! 

to  changes  in  temperature,  or  to  changes  in  moisture  content.  If 
the  soil  is  beaten  or  mixed  when  too  wet,  compound  particles  are 
destroyed  and  the  soil  dries  into  a  hard  compact  mass. 

Tilth  is  a  condition  of  the  soil,  and  only  indirectly  due  to  pro- 
cesses of  tillage.  A  heavy  soil  is  not  reduced  to  powder  by  the 
mechanical  force  exerted  through  implements.  Tillage  stirs  the 
soil,  and  places  it  so  that  natural  forces  exert  their  greatest  effect 
upon  it.  The  soil  in  good  tilth  falls  into  a  powder 
under  the  action  of  the  various  instruments.  Such  a  con- 
dition of  the  soil  is  very  desirable.  It  allows  the  preparation  of  a 
good  seed  bed ;  it  is  most  suitable  for  ensuring  the  best  conditions 
of  moisture,  temperature,  and  chemical  action  in  the  soil  during 
the  growth  of  the  plant.  The  maintenance  of  good  tilth  is 
especially  important  on  clay  soils. 

The  production  of  a  good  tilth,  and  the  permeability  of  a  clay 
soil  to  water,  depend  largely  upon  the  formation  and  maintenance 
of  compound  particles.  The  conditions  favorable  to  the  forma- 
tion of  compound  particles  are  also  favorable  to  the  coagulation 
of  clay.  Any  change  which  converts  the  clay  from  a  coagulated 
to  a  swelled  condition  is  necessarily  destructive  to  compound 
particles,  but  it  is  quite  possible  to  destroy  compound  particles 
without  affecting  the  coagulated  condition  of  the  clay. 

Relation  of  Physical  Composition  to  Adaptation  of  Crops. — The 

adaptation  of  different  crops  to  particular  kinds  of  soil  is  due  to 
different  needs  of  the  crops  for  moisture,  for  soil  atmosphere,  for 
temperature,  and  their  habits  of  root  growth.  The  differences  in 
physical  composition  cause  soils  to  respond  differently  to  these 
needs,  and  hence  vary  their  adaptation.  But  climatic  conditions  of 
rainfall,  temperature  and  situation,  modify  the  way  which 
the  soil  fulfills  these  conditions.  Under  similar  conditions,  and 
in  a  general  way,  there  is  a  relation  between  the  physical  character 
of  the  soil  and  its  adaptation  to  crops,  and  this  is  shown  by  the 
general  agricultural  practice  and  treatment  of  such  soils. 

The  relation  of  physical  character  to  adaptation  to  crops  is 
studied  by  ascertaining  the  kinds  of  crops  actually  grown  upon 
the  various  classes  of  soils,  and  how  well  they  thrive  on  them. 


92  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  relation  between  physical  character  and  adaptation  in  the 
soils  of  the  Atlantic  and  Gulf  Coastal  Plains,  as  ascertained  by 
field  agents  of  the  Bureau  of  Soils,1  is  as  follows : 

Sands. — These  soils  are  characterized  by  open  structure,  thor- 
ough drainage  and  warm  nature.  They  are  the  earliest  truck 
soils,  produce  light  yields,  and  are  not  well  adapted  for  general 
farming. 

Fine  Sands. — These  are  more  retentive  of  moisture  than  the 
sands,  mature  truck  ten  days  to  two  weeks  later,  and  give  heavier 
yields.  They  are  not  well  adapted  for  general  farming. 

Sandy  Loam  Soils. — These  are  the  medium  early  truck  and 
light  general  farming  soils  of  the  Atlantic  and  Gulf  Coastal  Plains. 
They  are  the  lightest  desirable  soils  for  general  farming,  are 
more  retentive  of  moisture  than  the  fine  sands,  and  mature  crops 
about  two  weeks  later.  In  general  farming,  crop  returns  are 
light. 

Fine  Sandy  Loams. — These  soils  are  adapted  to  medium  truck 
crops,  give  moderately  good  yields  of  vegetables,  and  give  average 
yields  of  general  farm  crops.  Cotton  matures  somewhat  later 
than  on  the  sandy  soil. 

Loams. — These  soils  produce  medium-late  truck  crops  and  are 
the  best  soils  for  general  farming  in  this  region.  They  are  easily 
kept  in  good  condition  of  tilth  and  are  very  retentive  of  moisture. 
Vegetables  mature  late  but  the  yields  are  good.  Small  grains  and 
grasses  do  well. 

Silt  Loams. — These  are  adapted  to  late  truck,  vegetables  for 
canning  purposes  and  for  heavy  farm  crops  or  for  special  pur- 
poses. Hay  does  well  on  this  type  of  soil. 

Clay  Loams. — These  are  too  stiff  and  too  late  in  maturing  crops 
for  vegetables.  A  small  number  of  farm  crops  is  adapted  to  this 
type.  Wheat,  oats,  rice,  forage  crops,  and  grass  do  well. 

Clays. — These  are  adapted  to  heavy  farm  crops,  such  as  wheat, 
grass;  rice,  and  forage  crops  for  ensilage.  Cultivation  is  difficult. 
Early  varieties  of  cotton  do  well  outside  of  boll  weevil  districts. 

A  specific  example  of  the  relation  between  the  use  made  of 
1  Bulletin  No.  78. 


PHYSICAL  COMPOSITION  AND  CLASSES  OF  SOILS 


93 


a  soil  and  its  physical  analysis,  is  shown  by  the  analyses  of  typical 
Maryland  subsoils  published  by  Whitney.1 

PHYSICAL  ANALYSES  OF  MARYLAND  SUBSOILS. 


Diameter 
of 
particles 

Early 
market 
garden 

Market 
garden 

Tobacco 
land 

Wheat 
soil 

Wheat 
and 
grass 

Grass 
and 
wheat 

Fine  gravel  
Coarse  sand  
Medium  sand  •  • 
Fine  sand  

2-1.0 
1.0-0.05 
0.5-0.25 
O  2^-O  IO 

0.5 
5-0 
4O.2 

27  6 

0.4 
2.O 
28.6 
•JQ  7 

1-5 

5-7 
13-3 

8  4. 

0.4 
0.6 

22  6 

O.2 

1-3 
4.0 

1-3 
0-3 
I.I 
I.o 

Very  fine  sand  • 
<^ilt 

O.IO-O.O5 

12.  1 

77 

11.4 
50 

15.0 

28  Q 

30.6 

14  o 

11.6 

•JQ   O 

6.9 

2Q  I 

Fine  silt 

2  2 

.«-» 

2  O 

7  8 

A     I 

11 

II  O 

Clav 

4      A 

8  8 

14  6 

22  O 

•12  7 

47   A 

The  early  market  garden  soil  contains  nearly  73  per  cent.  sand. 
It  has  little  power  of  retaining  water  and  is  therefore  warm  and 
dry.  It  produces  vegetables  about  ten  days  earlier  than  any  other 
soil  in  Maryland. 

The  market  garden  soil  contains  more  fine  sand  and  more  clay. 
It  is  more  productive  but  later  in  maturing  spring  crops  than  the 
soil  named  above.  It  is  superior  to  the  first  soil  for  peaches, 
small  fruit,  and  autumn  crops. 

The  tobacco  soils  contain  10  to  20  per  cent,  clay,  the  lighter 
soil  yielding  a  smaller  crop  but  a  better  quality  of  leaf.  The 
wheat  soils  are  somewhat  heavier.  The  wheat  soil  (No.  4)  is  the 
lightest  soil  upon  which  wheat  can  profitably  be  grown  in  Mary- 
land. The  soil  is  too  light  for  permanent  meadow  or  pasture 
and  too  heavy  for  the  best  quality  of  tobacco.  The  wheat  and 
grass  land  is  more  productive  than  the  wheat  soil.  The  grass  and 
wheat  soil  is  still  more  productive. 

Similar  relations  can  be  traced  for  other  soils,  between  the 
physical  composition  and  crops  adapted  to  them.  Other  factors 
come  into  play,  however,  such  as  the  location  of  the  soil,  its 
depth,  and  its  chemical  composition.  The  physical  properties  of 
a  soil  depend  upon  other  things  in  addition  to  its  physical  com- 
position, as  we  shall  see.  The  relation  between  soil  composition 
and  crop  adaptation  probably  depends  to  a  large  extent  upon 
1  U.  S.  Weather  Bureau,  Bulletin  No.  4. 


94 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


water  conditions,  which  is  largely  influenced  by  the  physical  com- 
position of  the  soil. 

Similar  relations  between  physical  character  and  crop  adaptation 
were  traced  in  England  by  Hall.1  He  found  very  heavy  soils 
generally  used  for  pasture.  Wheat  soils  are  heavy.  Barley  soils 
are  lighter  than  wheat  soils,  potato  soils  are  still  lighter.  Hop 
soils  are  somewhat  like  barley  soils.  Fruit  soils  are  lighter  than 
hop  soils.  The  different  kinds  of  fruit  have  their  own  require- 
ments. Waste  soils  are  characterized  by  large  amounts  of  coarse 
sand,  small  amounts  of  clay  and  fine  silt,  an  acid  reaction  and 
absence  of  calcium  carbonate. 

Analyses  of  typical  soils  used  for  various  crops  in  the  area 
studied  by  Hall  are  shown  in  the  table.  The  reader  will  notice 
that  the  groups  of  soil  particles  are  different  from  those  else- 
where mentioned  in  this  chapter. 


Wheat 

Barley 

Potatoes 

Hops 

Fruits 

Fine  gravel  above  i     mm 

1.4 

1.2 

0.9 

1.2 

1.0 

Coarse  sand       1-0.2        ' 

3-7 

18.3 

2O.  I 

4.8 

6.8 

Fine  sand       0.2-0.04 

24-5 

32.0 

43-5 

33-3 

42.0 

Silt                0.04-0.01 

23.0 

18.2 

II.  0 

28.3 

23-3 

Fine  silt        0.01-0.002 

12.8 

8.0 

6.4 

8.7 

'      7-3 

Clay  below   0.002 

20.8 

11.9 

9-7 

12.  1 

10.9 

The  subsoil  is  generally  heavier  in  texture,  or  contains  more 
clay,  than  the  surface  soil.  This  is  largely  due  to  the  action  of 
water  moving  the  finer  particles  of  the  soil  into  its  lower  portions. 

Soil  Types  and  Soil  Series. — A  soil  type  is  a  definite  soil,  with  a 
definite  physical  composition  and  other  definite  properties.  It 
may  vary  somewhat  in  different  parts  of  the  area,  but  in  all 
essential  respects,  it  is  the  same  soil. 

Soil  series  are  groups  of  soil  types  related  to  one  another 
through  source  of  material,  method  of  formation,  topographic 
position,  coloration,  and  other  characteristics.  The  soil  types  in 
the  series  vary  chiefly  in  physical  composition  and  other  char- 
acteristics caused  thereby.  A  soil  series,  to  be  complete,  would 

1  Jour.  Agr.  Sci.,  1911,  p.  206. 


PHYSICAL  COMPOSITION  AND  CLASSICS  OF  SOILS  95 

contain  all  the  possible  physical  classes  of  soils  already  mentioned. 
Comparatively  few  soil  series,  however,  are  complete. 

In  establishing  soil  types  and  soil  series,  the  texture  of  the  soil, 
its  mechanical  composition,  its  origin,  the  topography  of  the  soil, 
native  vegetation,  color,  depth,  drainage,  and  all  other  factors 
which  influence  the  relation  of  the  soil  to  the  crop,  are  considered, 
as  far  as  possible.  Both  the  surface  soil,  and  the  subsoil  should 
be  considered.  All  the  types  in  a  given  locality  have  been  formed 
by  the  same  general  processes,  and  will  naturally  grade  into  one 
another.  In  humid  regions,  the  description  of  a  type  covers  the 
material  to  an  average  depth  of  three  feet;  in  arid  regions  to  a 
depth  of  six  feet.  Minor  variations  of  texture,  structure,  organic 
matter  content,  or  succession  of  materials,  which  occur  in  sections 
representing  10  acres  or  less,  are  described  as  phases  by  the  field 
agents  of  the  Bureau  of  Soils.  There  is  some  local  variation  in 
types.  Differences  in  agricultural  value  may  be  due  to  differences 
in  treatment  of  the  same  soil. 

The  soil  name  of  a  type  does  not  mean  that  it  belongs  to  that 
class  necessarily.  For  example,  Norfolk  sandy  loam  may  be  a 
coarse  to  medium  yellow  or  gray  sand  or  light  sandy  loam. 

Pippin1  suggests  the  following  scheme  of  soil  classification. 
The  broadest  division  is  based  on  temperature,  into  (I)  tem- 
perate, (II)  subtropical,  (III)  tropical  regions.  Each  of  these  is 
sub-divided  into  (A)  humid,  (B)  semi-arid,  (C)  arid  sections 
based  on  rainfall.  The  next  two  sub-divisions  are  into  divisions 
and  provinces  according  to  mode  of  formation;  (a)  sedentary, 
soils  sub-divided  into  (a±)  residual  soils  and  (a2)  cumulose  soils 
and  (b)  transported  soils,  sub-divided  into  (&x)  colluvial,  (b.2) 
wind  borne,  (A,)  transported  by  water;  namely,  (b3a}  ocean, 
(£3*)  lakes,  (by)  rivers.  The  soils  of  different  origin  are  next 
divided  into  groups  based  on  the  source  of  material  (i)  acid  and 
basic  igneous  rock;  (2)  shale  and  slate;  (3)  sandstone  and 
quartzite;  (4)  limestone  and  marble  rock:  (5)  muck,  peat,  and 
swamps  (cumulose  soil).  The  next  sub-division  is  into  series, 
based  on  color,  organic  matter,  drainage,  lime  content,  and  special 
1  Proc.  Am.  Soc.  Agron.,  1911,  p.  88. 


96  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

chemical  properties.  Finally,  the  types,  or  individual  soils,  are 
based  on  texture  and  structure.  This  scheme  offers  good  possi- 
bilities; the  group,  acid  and  basic  igneous  rocks,  is,  however,  a 
broad  one  and  should  be  sub-divided. 

Some  Soil  Series. — Soil  types  numbering  715  have  been 
established  by  the  Bureau  of  Soils  of  the  United  States  Department 
of  Agriculture.  These  types  have  been  divided  into  86  series. 
A  full  list  and  description  of  these  types  and  series  is  found  in 
Bulletins  55  and  78  of  the  Bureau  mentioned.  The  following  are 
a  few  series,  mentioned  for  the  sake  of  illustration. 

Atlantic  and  Gulf  Coastal  Plains. — Houston  Series. — Dark-gray 
or  black  calcareous  prairies.  One  of  the  most  productive  series 
for  upland  cotton,  and  well  adapted  to  alfalfa  and  other  forage 
crops. 

Norfolk  Series. — Light-colored  soils  with  yellow  sand  or  sandy 
clay  subsoils.  This  series  contains  some  of  the  most  valuable 
truck  soils  of  the  Atlantic  and  Gulf  Coast  States,  and  certain 
members  of  the  series  are  adapted  under  certain  climatic  condi- 
tions to  wheat,  grass,  tobacco,  and  fruit. 

Orangeburg  Series. — Light-colored  soils  with  red  sandy  clay 
subsoils.  This  series  constitutes  some  of  the  best  cotton  soils  of 
the  South,  and  certain  members  of  the  series  are  particularly 
adapted  to  tobacco. 

Portsmouth  Series. — Dark-colored  soils  with  yellow  or  mottled 
gray  sand  or  sandy  clay  subsoils.  Where  drainage  is  adequate, 
this  series  is  adapted  to  some  of  the  heavier  crops,  to  small  fruits, 
and  to  Indian  corn. 

Susquehanna  Series. — Gray  soils  with  heavy  red  clay  subsoils 
which  become  mottled  and  variegated  in  color  in  the  deep  subsoil. 
Only  one  member  of  the  series,  the  sandy  loam,  has  been 
developed  to  any  considerable  extent.  This  one  is  used  for  fruit 
and  general  farm  purposes,  but  the  other  members  are  particu- 
larly refractory  and  difficult  to  bring  into  a  productive  state. 

River  Flood  Plain. — Miller  Series. — Brown  to  red  alluvial  soils 
formed  from  the  reworking  of  materials  derived  from  the 
Permian  Red  Beds.  Very  productive  soils,  suitable  for  cotton, 


PHYSICAL  COMPOSITION  AND  CLASSES  OF  SOILS  97 

corn,  sugar-cane,  alfalfa,  and  vegetables;  especially  adapted  to 
peaches. 

W abash  Series. — Dark-brown  or  black  soils  subject  to  over- 
flow. Very  productive  soils,  used  for  cotton,  sugar-cane,  corn, 
wheat,  oats,  grass,  alfalfa,  sugar  beets,  potatoes,  and  other 
vegetables. 

Piedmont  Plateau. — Cecil  Series. — Gray  to  red  soils  with 
bright-red  clay  subsoils,  derived  from  igneous  and  metamorphic 
rocks.  Constituting  by  far  the  larger  portion  of  the  plateau, 
these  soils  are  well  adapted  to  and  are  used  for  cotton,  export 
tobacco,  and  fruit,  and  the  lighter  members  for  truck  crops.  As 
a  rule  they  are  not  highly  developed,  but  where  properly  handled, 
the  heavier  members  produce  excellent  crops  of  corn  and  grazing 
and  hay  grasses. 

Appalachian  Mountains  and  Plateau. — Dekalb  Series. — Brown 
to  yellow  soils  with  yellow  subsoils,  derived  from  sandstones  and 
shales.  Soils  of  this  series  are  used,  according  to  texture,  eleva- 
tion, exposure,  and  character  of  surface,  either  for  the  production 
of  hay,  for  pasture,  or  for  orchard  and  small  fruit. 

Porters  Series. — Gray  to  red  soils  with  red  clay  subsoils, 
derived  from  igneous  and  metamorphic  rocks.  This  is  the 
most  important  series  for  mountain  fruits  of  the  eastern  United 
States.  It  is  also  used  for  general  farming. 

Limestone  Valleys  and  Uplands. — Clarksville  Series. — Light- 
gray  to  brown  soils  with  yellow  to  red  subsoils,  derived  mainly 
from  the  St.  Louis  limestone.  Apples  and  peaches  are  com- 
mercially important.  Tobacco  is  a  leading  product. 

Cumberland  Series. — Brown  surface  soils,  derived  from  the 
deposit  of  sedimentary  material  overlying  residual  limestone  sub- 
soils. Used  for  cotton  and  other  general  farm  crops,  truck,  and 
fruit. 

Glacial  and  Loessial  Regions. — Marshall  Series. — Dark-colored 
upland  prairie  soils.  The  principal  soils  of  the  great  corn  belt 
belong  to  this  series,  while  in  the  Northwest  the  finest  wheat  soils 
are  found  in  this  group.  They  are  among  the  best  general  farm- 
ing soils  of  the  entire  country. 


98  PRINCIPLES  OF  AGRI CULTURAL  CHEMISTRY 

Miami  Series. — Light-colored  upland  timbered  soils.  The 
different  members  of  this  series  are  considered  good  general  farm- 
ing soils  and  have  in  addition  special  adaptations  for  truck,  small 
fruit,  and  alfalfa. 

Glacial,  Lake  and  River  Terraces. — Clyde  Series. — Dark-colored 
swamp  soils  formed  from  reworked  glacial  material  deposited  in 
glacial  lakes.  A  special  use  for  these  soils  is  the  production  of 
sugar  beets,  while  general  farm  crops,  truck,  and  canning  crops 
are  grown  extensively. 

Fargo  Series. — Black  calcareous  soils  rich  in  organic  matter 
formed  by  deposition  of  material  in  glacial  lakes.  This  is  the 
most  important  group  of  soils  in  the  Red  River  Valley,  and 
includes  exceptional  soils  for  the  production  of  wheat,  barley,  and 
flax. 

Residual  Soils  of  the  Western  Prairie  Region. — Crawford 
Series. — Brown  soils  with  reddish  subsoils,  derived  from  lime- 
stones. The  soils  of  this  series  range  from  rough  areas  suited 
mainly  for  pastures  to  fertile  general  farming,  fruit-growing,  and 
trucking  soils. 

Great  Basin. — Bingham  Series. — Porous  dark  or  drab  colluvial 
and  alluvial  soils  underlaid  by  gravel  or  rock,  occupying  lower 
mountain  slopes.  The  lighter  types,  when  irrigable,  are  devoted 
to  orchard  fruits,  and  the  heavier  types,  to  alfalfa  and  sugar  beets. 

Northwestern  Intermountain  Region. — Bridger  Series. — Dark- 
colored  soils  with  sticky  yellow  subsoils,  of  colluvial  and  alluvial 
origin.  These  soils  generally  occupy  elevated  foot  slopes  or 
sloping  valley  plains  and  have  not  been  developed  to  a  great 
extent.  They  are  most  extensively  used  for  the  production  of 
grain,  and  when  irrigated,  are  utilized  in  the  production  of  alfalfa 
and  other  hay  crops ;  under  favorable  climatic  conditions  they  are 
adapted  to  fruits. 

Rocky  Mountain  Valleys,  Plateaus,  and  Plains. — Billings  Series. 
— Compact  adobe-like  gray  to  dark  or  brown  soils  and  subsoils, 
formed  mainly  by  reworking  of  sandstones  and  shales  and 
occupying  old  elevated  stream  terraces.  This  is  an  important 
series  adapted  to  alfalfa  and  general  farm  crops  and  stock  raising; 


PHYSICAL  COMPOSITION  AND  CLASSES  OF  SOILS 


99 


also  used  to  a  considerable  extent  in  the  production  of  sugar  beets. 

Arid  Southwest. — Gila  Series. — Light  to  dark  brown  soils  of 
flood-plain  alluvium  underlaid  at  varying  depths  by  coarse  sands 
and  gravels.  Under  favorable  irrigation  and  drainage  conditions, 
the  members  of  the  Gila  series  are  adapted  chiefly  to  the  produc- 
tion of  alfalfa,  potatoes,  truck,  and  root  crops. 

Pacific  Coast. — Fresno  Series. — Light-colored  soils  with  light- 
gray,  ashy  subsoils  and  alkali-carbonate  hardpan,  derived  from 
old  alluvial  wash.  Where  protected  from  alkali  accumulations, 
these  soils  have  been  very  successfully  used  for  vineyards  and 
raisin  grapes,  and  are  particularly  adapted  to  almonds,  peaches, 
and  apricots. 


I 

•££. 

V  *-'%.; 

I 

x:;Kl 


Fig.  28. — Photograph  of  a  soil  map,  Willis  area,  Texas. 


Soil  Survey. — The  soil  surveyor  is  provided  with  a  map,  com- 
pass, measuring  instruments,  and  soil  sampler.  After  a  general 
inspection  has  been  made,  and  the  provisional  types  decided  upon, 
the  mapping  is  begun.  Preliminary  borings  in  the  soil  are  made 
to  outline  the  location  of  a  body  of  soil  of  uniform  character. 
This  is  then  colored  in  on  the  map.  The  surveyor  then  works 
away  from  this  area  until  a  different  type  of  soil  is  encountered. 


100  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  line  of  separation  between  these  two  types  (which  may 
consist  of  a  narrow  strip  of  intermediate  soil)  is  then  outlined  on 
the  map.  Other  areas  are  outlined  in  the  same  manner. 

The  identification  of  the  types  is  aided  by  physical  analysis. 
It  is,  of  course,  not  possible  to  make  a  great  number  of  types  in  a 
given  area,  and  a  certain  latitude  must  be  allowed,  between  which 
limits  the  soil  may  vary.  As  a  rule  the  different  types  of  soil  and 
their  properties  are  very  well  known  to  the  farmers  in  the  area 
surveyed.  So  far  the  types  have  been  largely  based  upon  physical 
differences  as  observed  by  the  surveyor,  with  no  great  emphasis 
on  the  physical  analysis. 

Value  of  Soil  Survey. — A  soil  survey  outlines  the  various  types 
of  soil  in  the  area  surveyed,  shows  their  extent  and  relative 
importance,  and  exhibits,  to  some  extent,  the  soil  problems  of  the 
locality.  It  also  indicates  the  adaptation  of  the  various  types  of 
soil  to  different  crops. 

A  soil  survey  should  not  be  considered  as  an  end  in  itself,  but 
as  a  means  of  ascertaining  the  various  types  of  soil  in  the  area, 
as  a  basis  for  further  study.  Thorough  chemical,  physical, 
bacteriological,  and  other  studies  should  then  be  made  of  the 
various  types  of  soils.  The  results  of  these  studies  can  then  be 
applied  to  definite  areas. 

Soil  surveys  also  show  what  crops  may  possibly  be  grown  upon 
the  various  types  of  soil  in  question.  Information  secured  upon 
the  same  types  in  other  districts,  may  be  made  available.  Results 
of  fertilizer  experiments  made  upon  definite  types  of  soil  can  be 
applied  to  similar  types  of  soils  elsewhere,  but  not  indis- 
criminately, as  has  been  too  often  done.  Other  experimental 
work  can  also  be  definitely  applied  to  the  kind  of  soil  on  which  it 
is  carried  out.  Relations  between  the  various  types  should  be 
traced  so  that  work  on  one  type  may  be  applied  to  other  types. 


CHAPTER  VI. 


PHYSICAL  PROPERTIES  OF  SOILS. 

The  soil  affects  the  growth  of  the  plant  through  both  physical 
and  chemical  properties,  which  react  upon,  and  modify  one 
another.  The  chief  physical  conditions  which  affect  the  plant  are 
the  depth  of  the  soil,  its  temperature,  the  amount  of  water  it 
supplies,  and  the  composition  of  the  soil  atmosphere.  These  are 
modified  by  a  variety  of  factors.  The  chief  chemical  condition 
which  affects  plants  is  the  supply  of  plant  food,  but  this  supply 
is  to  some  extent  dependent  upon  physical  factors.  The  chemical 
composition  of  the  soil  has  other  effects  upon  plants.  It  affects 
the  physical  character  of  the  soil.  It  is  related  to  the  condition 
of  the  soil  as  regards  neutrality,  and  the  absence  or  presence 
of  injurious  substances,  which  also  modify  the  relation  of  soil  to 
plants. 

The  physical  and  chemical  properties  of  the  soil  are  closely 
related,  and  are  more  or  less  dependent  upon  one  another.  They 
cannot  be  entirely  separated  without  presenting  a  very  one-sided 
view  of  the  functions  of  the  soil. 

Soil  and  Subsoil. — Going  down  into  the  soil  from  the  surface, 
we  generally  find  the  following  layers :  First,  the  top,  or  surface 
soil,  varying  from  3  inches  to  a  foot  or  more  in  depth,  and  usually 
darker  in  color  than  the  layers  below.  Next  is  the  subsoil,  from 
a  few  inches  to  several  feet  in  depth.  If  the  soil  is  sedentary, 
below  this  is  a  mixture  of  rock  fragments  and  soil,  and  then  comes 
the  rock  of  the  locality,  the  upper  layers  of  which  are  decom- 
posed and  rotten.  Sometimes  the  layer  of  soil  rests  directly  upon 
the  solid  rock.  Sometimes  the  surface  soil  has  been  washed 
away,  leaving  the  unproductive  subsoil. 

The  surface  soil  is  distinguished  from  the  subsoil  by  its  darker 
color,  due  to  the  decaying  vegetable  matter  contained  in  it, 
derived  from  roots  and  plant  residues.  The  depth  of  the  surface 
soil  is,  in  humid  climates,  often  determined  by  the  depth  of 
plowing,  and  is  generally  from  4  to  12  inches. 

A  different  definition  of  soil  and  subsoil  is  used  by  the  Bureau 


IO2  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

of  Soils.  The  surface  soil  is  the  upper  layer  of  the  earth,  and 
continues  until  there  is  a  decided  change  in  physical  character. 
In  other  words,  the  distinction  between  soil  and  subsoil  is  based 
upon  differences  in  mechanical  composition. 

In  humid  sections,  the  subsoil  is  not  well  suited  for  the  growth 
of  plants.  If  it  is  exposed  by  removal  of  the  surface  soil,  it  is 
in  most  cases  unproductive  until  it  has  been  subjected  to 
atmospheric  influences  for  some  time.  Organic  matter  added  to 
the  soil,  such  as  manure,  is  said  to  aid  in  converting  the  raw  sub- 
soil into  productive  soil.  If  too  much  subsoil  is  mixed  with  the 
surface  soil,  by  deep  plowing,  the  productiveness  of  the  soil  may 
be  decreased.  In  arid  regions,  according  to  Hilgard,1  the  soil  is 
suitable  for  plants  to  the  depth  of  three  to  ten  feet,  or  more. 
Material  from  the  depth  of  eight  feet  has  been  put  on  gardens 
and  served  well  the  first  year.  In  preparing  land  for  irrigation, 
the  land  is  leveled  without  regard  to  the  subsoil,  and  no  bad 
effects  are  noticed.  These  practices  would  be  injurious  to  humid 
soils.  The  difference  is  due  to  the  greater  depth  of  penetration 
of  air  and  the  roots  of  plants,  under  arid  conditions. 

Penetration  of  Roots. — The  depth  to  which  roots  penetrate 
into  the  soil  depends  upon  the  condition  of  the  soil  and  subsoil, 
the  climate,  and  the  kind  of  plant.  The  roots  of  plants  grown  in 
humid  regions  penetrate  only  a  comparatively  short  distance.  In 
arid  climates  it  is  necessary  that  the  roots  penetrate  deeply,  in 
order  that  they  may  endure  drought. 

According  to  Hilgard,  the  roots  of  the  hop  have  been  found,  in 
arid  climates,  to  penetrate  to  the  depth  of  18  feet;  roots  of  wheat 
and  barley  may  reach  to  4  to  7  feet  in  sandy  soil ;  roots  of  grape 
vines  have  been  found  at  the  depth  of  22  feet  below  the  surface. 
Thus  in  arid  climates,  where  a  drought  of  five  or  six  months  pre- 
vails during  the  growing  season,  the  roots  of  plants,  by  penetrating 
to  considerable  distances,  will  secure  water  in  the  depths  of  the 
soil.  The  depth  to  which  plants  send  their  roots  affects  the 
quantity  both  of  water  and  of  plant  food  at  their  disposal.  Differ- 
ences in  the  needs  of  plants  for  food  may,  in  part,  be  due  to 
1  The  Soil,  p.  163. 


PHYSICAL,  PROPERTIES  OF  SOILS 


103 


differences  in  rooting  habits.  Further,  the  character  of  root 
growth  is  also  related  to  the  kind  of  tillage  which  should  be  given. 
Crops  whose  roots  extend  near  the  surface  of  the  soil  should 
not  have  these  roots  cut  by  deep  cultivation. 


Fig.  29. — Distribution  of  roots  of  corn,  Kansas. 

Exhibition  specimens  of  roots  are  secured  in  the  following 
manner.1  A  block  of  soil  is  cut  out,  with  the  plant  in  the  center, 
and  a  wooden  frame  covered  with  one-half  inch  mesh  wire  netting 
is  slipped  over  it.  Plaster  of  Paris  paste  is  then  poured  on  the 
top  to  hold  the  plant  and  large  numbers  of  sharpened  wires  are 
pushed  through  the  soil  and  fastened  to  the  netting,  to  hold  the 
1  Kansas  Bulletins  75,  127;  North  Dakota  Bulletin  43,  64. 


IO4  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

roots  in  place.     When  the  plaster  hardens  the  dirt  is  washed  away 

by  a  stream  of  water. 

Sanborn1  drove  an  iron  frame  into  the  soil,  removed  the  soil  in 

layers  of  one  inch  to  the  depth  of  a  foot,  and  washed  out  the 

roots.     The  roots  were  dried  and  weighed  in  order  to  ascertain 

their  distribution  in  the  soil  layers. 

At  the  Arkansas  Experiment  Station,2  plants  were  grown  in 

boxes  10  by  12  inches  and  4  feet  deep,  and  the  quantity  of  roots 

in  different  layers  of  the  soil  was  determined.     These  conditions 

are  somewhat  artificial,  and  the  roots  would  probably  penetrate 

deeper  than  in  a  natural  soil. 

The  results  of  the  preceding  experiments  are  summarized  in 

the  following  table : 

Barley  96  per  cent,  of  roots  in  first    7  inches  (Utah) 

Corn 90       "  "         7 

Corn 93       "  "  "         7 

Clover  4  years  old -.  94       "  "7 

Clover Evenly   distributed   between   the  first   2   feet 

(Arkansas). 

Millet 80  per  cent,  in  the  first  12  inches  (Arkansas) 

Oats 96       "  "  7       "        (Utah) 

Orchard  grass   90       "  20  (Arkansas) 

Peas Mostly  in  12  to  18  inches  of  soil 

Potatoes 70  per  cent,  in  7th  to  i3th  inch  (Utah) 

Timothy 87        "  in  first  7  inches  (Utah) 

Timothy 95        •'  "        6       "        (Arkansas) 

Wheat 92        "  "        7       "         (Utah) 

It  appears  that  barley,  corn,  oats,  timothy,  and  wheat  developed 
over  86  per  cent,  of  their  roots  in  the  first  seven  inches  of  soil. 
Most  of  the  plant  food  and  water  which  they  take  up  must 
necessarily  be  drawn  from  this  layer.  Clover,  millet,  peas, 
orchard  grass,  and  potatoes  appear  to  send  their  roots  deeper,  but 
these  results  (with  the  exception  of  the  potatoes)  are  from  the 
Arkansas  Station,  where  the  plants  were  grown  in  boxes  and  not 
in  the  free  soil.  Plants  grown  in  boxes,  as  in  the  Arkansas 
Experiment,  would  have  a  tendency  to  send  their  roots  deeper 
than  plants  grown  in  the  natural  soil,  on  account  of  the  pulveriza- 

1  Utah  Experiment  Station,  Bulletin  32. 

2  Bulletin  29. 


PHYSICAL  PROPERTIES  OF  SOILS  IO5 

tion  and  exposure  to  the  atmosphere  that  the  soil  received  in  fill- 
ing the  boxes,  and  also  because  the  boxes  were  probably  under- 
drained. 

Other  experiments  made  at  the  Kansas,  New  York,  North 
Dakota,  Iowa,  and  Minnesota  Stations,  show  that  the  greatest 
proportion  of  the  roots  of  plants  develop  in  the  surface  foot  of 
the  soil,  but  appreciable  quantities  of  roots  may  penetrate  much 
deeper.  These  experiments  were  qualitative.  Further  quantita- 
tive experiments  are  needed,  as  it  is  very  important  for  scientific 
soil  studies,  to  know  the  quantitative  distribution  of  the  roots  of 
various  plants  in  various  soil  types  and  in  various  sections  of  the 
country. 

The  depth  to  which  roots  of  some  plants  may  penetrate  is 
shown  in  the  following  table,  taken  from  experiments  made  in 
Kansas  and  North  Dakota.  The  subsoil  was  in  some  cases  a 
stiff,  clay  soil. 

DEPTH  OF  PENETRATION  OF  ROOTS  OF  PLANTS. 
Alfalfa 6      to  10  feet.         Clover  2^  feet. 


Corn 2>^  to  6 

Grasses 2^  to  3 

Millet 2      to  3 

Oats 4 

Rye 3 

Sugar  beet 3^  to  4 


Cowpeas 3 

Kaffir  corn...  3^  to  5 

Milo  maize  •  •  3^  to  4 

Potatoes 3 

Sorghum 3  %  to  4 

Wheat 4 


Effect  of  Depth  of  Soil  on  Plants. — The  depth  to  which  the 
roots  of  plants  penetrate  depends  both  upon  the  character  of  the 
soil  and  the  habit  of  the  plant.  The  roots  of  plants  can  penetrate 
easily  in  a  sandy  subsoil,  but  may  have  difficulty  in  entering  heavy 
clay. 

In  general,  the  deeper  the  roots  can  penetrate  the  soil,  the 
better  the  growth  of  the  crop.  Roots  which  occupy  12  inches  of 
soil  will  have  twice  as  much  soil  to  draw  upon  for  moisture  and 
for  plant  food,  as  those  which  occupy  only  6  inches.  They  will 
also  have  twice  as  much  space  in  which  to  expand  their  roots. 

The  experiments  of  Lemmerman1  may  be  cited  as  showing  the 
effect  of  root  space  upon  plant  growth.    He  grew  mustard  in  pots 
of  the  same  surface  area,  but  of  different  depths.     One  vessel  of 
1  Jahresber.  f.  Agr.  Chem.,  1903,  p.  42. 
8 


io6 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


each  size  received  no  fertilizer,  and  one  of  each  size  received  I, 
2,  and  3  grams  fertilizer  respectively.    The  results  are  as  follows : 

WEIGHT  OF  CROP  IN  DIFFERENT  SIZED  VESSELS. 


Fertilizer 

I«arge  vessel 

Small  vessel 

Grams 

26  8 

Grains 
IQ  7 

do  ^ 

•26  2 

7    S 
61  i 

47  8 

62  i 

A8  T. 

The  increase  of  fertilizer  from  2  to  3  grams  had  little  effect 
upon  the  crop  in  the  pots  of  either  size.  That  is,  the  limiting 
condition  is  the  size  of  the  pot.  The  crop  in  the  large  pot  is  con- 
siderably larger  than  in  the  small  one ;  this  shows  that  the  space 
occupied  by  the  roots  has  considerable  influence.  However,  this 
difference  may  be  due  to  differences  in  moisture  content. 

Limitations  of  Soil  Depth. — The  depth  of  the  surface  soil,  as 
stated,  is  largely  dependent  upon  the  depth  of  plowing.  The  sur- 
face and  subsoil  together  may  be  so  shallow  as  to  interfere 
seriously  with  the  productiveness  of  the  soil.  The  limiting  condi- 
tion may  be  hard  pan,  the  water  table,  rock,  or  heavy  subsoil. 

Hard  pan  is  a  layer  of  hard  earth,  sometimes  rock-like,  which 
cannot  be  penetrated  by  plant  roots.  Hard  pan  may  be  caused  by 
constant  plowing  at  the  same  depth.  The  sole  of  the  plow  con- 
solidates the  layer  of  soil  on  which  it  slips.  Such  hard  pan  is 
most  liable  to  occur  in  heavy  clay  soils.  Hard  pan  may  also  be 
caused  by  deposition  of  matter  from  drainage  or  irrigation  waters. 
The  deposited  matter  cements  the  soil  grains  into  rocky  masses. 
The  cement  is  usually  carbonate  of  lime,  but  sometimes  it  is  an 
iron  cement,  or  a  humate. 

Hard  pan  may  be  prevented  by  varying  the  depth  of  plowing, 
or  by  an  occasional  subsoiling.  It  is  particularly  liable  to  occur 
in  arid  climates.  In  some  localities  it  should  be  destroyed  with 
dynamite  or  other  explosives  before  fruit  trees  are  set  out. 

Rock,  when  too  near  the  surface,  forbids  the  use  of  the  soil  for 


PHYSICAL  PROPERTIES  OF  SOILS  lO/ 

cultivated  crops,  though  the  land  may  possibly  be  used  for  timber 
or  grazing. 

The  water  table, -when  too  near  the  surface,  converts  the  soil 
into  a  swamp.  When  somewhat  lower,  the  soil  is  suitable  for 
some  plants,  but  is  too  wet  for  agricultural  purposes.  If  from 
4  to  6  feet  below  the  surface,  the  soil  is  suitable  for  cultivation, 
but  the  water  table  is  often  considerably  lower  than  this. 

In  arid  climates  a  proper  substratum  is  much  more  important 
than  in  humid  climates,  since  the  roots  must  be  able  to  penetrate 
deeply  in  order  to  endure  drought.  Hilgard1  gives  the  following 
examples  of  faulty  substrata  found  in  California. 

A.  The  surface  soil  of  about  12  inches  is  underlaid  by  horizon- 
tal layers  of  shale.     This  soil  might  possibly  be  rendered  useful 
by  blasting  with  explosive. 

B.  The  surface  soil  of  12  inches  is  underlaid  by  a  heavy  red 
clay,  which  can  hardly  be  penetrated  by  roots.     After  blasting 
with   dynamite  this   soil   has  been   used   successfully.     Without 
blasting,  orchards  die  in  about  three  years. 

C.  This  soil  has  a  calcareous  hard  pan  at  the  depth  of  about 
four  feet.     On  account  of  the  arid  climate,  the  roots  of  trees  must 
be  able  to  penetrate  to  a  greater  depth  than  this. 

D.  The  water  level  is  about  three  feet.     This  prevents  root 
penetration  and  restricts  the  use  of  the  soil  to  shallow  rooted 
crops.     This  condition  may  arise  from  the  leakage  of  water  from 
irrigation  ditches. 

E.  The  soil  is  underlaid  by  a  layer  of  coarse  sand  or  gravel  at 
the   depth   of   about   four   feet,   through   which   roots   will   not 
penetrate  to  the  water  below.     A  large  number  of  orchards  have 
died  from  this  cause. 

Soil  Temperature. — Processes  of  plant  and  animal  life  can  go 
on  only  between  certain  limits  of  temperature.  The  temperature 
to  which  the  plant  is  subject  depends  upon  both  the  soil  and 
atmospheric  conditions,  the  latter  being  perhaps  the  controlling 
factor. 

1  The  Soil,  p.  177. 


io8 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


The  earlier  the  soil  warms  up  in  the  spring,  the  earlier  it  can  be 
planted.     Some   few  seeds  begin  to  germinate   at  the   freezing 


Fig.  30. — Fruit  grown  against  a  wall  so  that  it  will  ripen.     France, 
point,  but  most  seeds  require  a  higher  temperature.     Haberlandt1 
1  Landw.  Versuchs-stat.,  17,  p.  104. 


PHYSICAL  PROPERTIES  OF  SOILS 


109 


tested  various  seeds  at  several  temperatures  and  found  the  lowest 
temperature  at  which  germination  took  place  was  as  follows : 
Alfalfa,  beets,  barley,  beans,  red  clover,  oats,  peas,  turnips,  wheat  •  •   32-40°  F. 

Indian  corn,  carrots,  sorghum,  sunflower,  timothy 40-51°  F. 

Cucumbers,  melons 60-65°  F. 

The  time  required  for  germination  decreases  as  the  temperature 
rises,  until  the  optimum  temperature  is  reached.  For  example, 
corn  required  11%  days  to  germinate  at  50°,  3>4  days  at  60°,  and 
3  days  at  65°  F.  While  the  sunflower  seeds  required  25  days  at 
51°,  at  60°  they  required  only  3  days  to  germinate. 

The  growth  of  the  plant  also  depends  upon  the  temperature  to 
which  it  is  subjected.  Between  the  extremes  of  heat  and  cold 
fatal  to  plants,  is  an  optimum  temperature,  varying  for  different 
plants,  at  which  the  maximum  growth  takes  place.  For  example, 
Bialablocki1  grew  rye,  barley,  and  wheat  20  days  at  different  soil 
temperatures,  and  determined  the  dry  matter  produced,  with  the 
following  results : 

WEIGHT  OF  PLANTS  GROWN  AT  DIFFERENT  TEMPERATURES. 


Temperature 

Rye 

Barley 

Wheat 

Degrees 


Mg. 
27,.  Q 

MR. 
17  I 

Mg. 

IS  8 

20  8 

18.0 

*O'<-> 

20  8 

•*2  4 

•14  A 

20  «: 

I5  

4Q  5 

T>6.7 

•JQ  8 

42  4 

42  o 

A*J    Q 

25  

47  O 

-7C    O 

4^-y 

d6  Q 

3°  

-21   2 

26  1 

4O  1 

4°  

In  this  experiment,  20°  was  the  most  favorable  temperature  for 
rye,  25°  for  barley,  and  30°  for  wheat.  The  wheat  plant  grown 
at  30°  is  three  times  as  large  as  that  at  8°  C. 

The  temperature  of  the  soil  has  a  direct  influence  not  only  upon 
the  plant,  but  upon  processes  in  the  soil,  especially  those  relative 
to  the  preparation  of  soil  nitrogen  for  plant  food. 

Factors  which  Influence  Soil  Temperature. — The  temperature 
of  the  soil  varies  to  a  certain  extent  with  that  of  the  air,  but  the 
1  Jahresber  f.  Agr.  Chem.,  1870-72,  p.  190. 


no 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


changes  are  slower  and  more  restricted  in  depth.  The  tempera- 
ture of  the  soil  is  influenced  by  its  color,  water  content,  location, 
composition,  etc. 

Location. — The  following  figure  illustrates  the  effect  of  location 
upon  the  light  and  heat  received  by  the  soil  from  the  sun.  Let  E 
and  F.  represent  two  equal  beams  of  sunlight,  falling  upon  the 
south  (A  B)  and  the  north  (C  D)  side  of  a  hill.  It  is  evident 


Fig.  31.— The  south  side  of  a  hill  receives  more  heat  than  the  north. 

that  the  ray  F  is  distributed  over  more  surface  than  the  ray  E  and 
that  its  heat  has  a  greater  area  to  warm.  The  soil  on  the  north 
side  thus  receives  less  heat  than  that  on  the  south  side.  The 
difference  depends  on  the  situation  of  the  sun,  and  the  inclination 
of  the  hill.  It  is  for  this  reason  that  the  south  sides  of  hills  in 
northern  regions  may  be  green  with  vegetation  while  the  north 
side  is  covered  with  snow.  A  wall  or  hedge,  by  protecting  the 
soil  from  wind,  or  by  reflecting  heat  upon  it,  may  cause  the  soil 
to  be  warmer.  Maligoti  arid  Durocher  found  the  average  soil 


PHYSICAL  PROPERTIES  OF  SOILS  III 

temperature  on  the  south  of  a  garden  wall  8°  C.,  higher  than  on 
the  north  side.  In  cool  climates,  fruits  which  refuse  to  ripen 
under  ordinary  conditions  may  attain  perfection  when  trained 
against  the  sunny  side  of  a  wall. 

Water  Content. — The  quantity  of  heat  required  to  raise  the 
temperature  of  the  soil  depends  upon  the  materials  of  which  it  is 
composed,  but  it  increases  with  the  quantity  of  water  present. 
Approximately  five  times  as  much  heat  is  required  to  raise  the 
temperature  of  one  pound  of  water  one  degree  as  for  one  pound 
of  soil.  Since  wet  soil  does  not  warm  up  as  rapidly  as  a  dry  soil, 
draining  a  wet  soil  makes  it  warmer,  as  a  general  rule.  Clay 
soils,  since  they  contain  more  water,  do  not  warm  up  as  quickly 
as  sandy  soils,  which  retain  much  less  water.  This  is  probably 
the  reason  sandy  soils  are  so  much  better  suited  to  early  truck 
crops  than  are  clay  soils.  They  warm  up  quicker,  and  maintain  a 
higher  temperature  during  the  early  part  of  the  year,  thereby 
forcing  the  growth  of  the  crop. 

The  evaporation  of  water  from  wet  soils  also  makes  them 
colder  than  dry  soils,  as  water  in  passing  into  the  form  of  a  vapor 
takes  up  considerable  amounts  of  heat.  King  found  that  a  clay 
soil  was  4°  to  7°  F.  lower  in  temperature  than  a  sandy  soil. 

Color. — The  color  of  the  soil  has  an  effect  upon  its  tempera- 
ture. A  dark  soil  warms  up  more  rapidly  than  a  light  one,  pro- 
vided they  contain  an  equal  quantity  of  water  and  other  con- 
ditions are  equal.  Schubler  exposed  two  layers  of  the  same  soil 
to  the  sun,  under  the  same  conditions,  making  one  white  by  means 
of  a  thin  layer  of  magnesia,  and  the  other  black  with  lampblack. 
The  temperature  of  the  blackened  soil  became  13°  to  14°  higher 
than  that  of  the  whitened  one.  Lampadius  has  given  the  soil  a 
coating  of  coal  dust  an  inch  thick  to  aid  in  ripening  melons,  and 
in  Belgium  and  Germany  it  is  found  that  the  grape  matures  best 
on  certain  soils  covered  with  gray  slate.  These  fragments,  how- 
ever, retain  the  heat  through  the  night.  Black  soils  often  contain 
more  water  than  light  soils,  and  the  light  soils  therefore  warm 
up  first. 

Organic   matter,   in   decaying,   gives   off   heat.     This   heat   is 


112  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

utilized  in  preparing  hot  beds  with  manure  and  earth.  The  decay 
of  the  manure  raises  the  temperature  of  the  hot  bed. 

The  quantity  of  organic  matter  in  the  soil  is  seldom  sufficient 
to  affect  its  temperature  to  a  practical  extent.  An  application  of 
10  tons  of  partly  decayed  manure  per  acre  may  raise  the  tempera- 
ture of  the  soil  2°  F.  for  the  first  five  days,  i°F.  for  the  second 
five  days,  and  0.6°  F.  the  third.  This  is  according  to  the  experi- 
ments of  -Georgeson.1  This  increase  in  temperature  might  aid  in 
hastening  the  germination  of  seeds  and  in  protecting  a  spring  crop 
from  frost. 

Wagner  found  an  average  increase  of  temperature  0.7  to  0.2° 
F.  during  four  to  twelve  weeks,  due  to  heavy  applications  of 
manure  under  field  conditions. 

Control  of  Temperature. — Artificial  regulation  of  temperature 
is  practiced  comparatively  little  in  agriculture,  though  of  con- 
siderable importance  in  horticulture,  in  which  hot  beds,  cold 
frames,  and  green  houses  are  used.  The  growth  of  tomato  plants, 
sweet  potato  vines,  and  other  plants  under  glass  or  in  protected 
places,  for  transplanting  when  the  soil  becomes  sufficiently  warm 
or  danger  of  frost  is  past,  is  a  kind  of  regulation  of  temperature. 
In  some  regions,  smoke  fogs  are  produced  to  prevent  frost  and 
thereby  protect  tender  plants,  or  plants  at  critical  stages  of 
growth. 

Color  of  Soils. — Soils  range  in  color  from  almost  pure  white, 
through  yellow,  red,  or  gray,  to  black.  The  yellow  or  red  colors 
are  due  usually  to  hydrated  oxides  of  iron.  Organic  matter  gives 
a  soil  a  black  color  when  wet,  or  a  gray  or  brown  or  black  color 
when  dry.  The  color  thus  affords  some  indication  as  to  the  char- 
acter of  the  soil.  Black  or  red  soils  are  generally  preferred  by 
practical  farmers.  The  intensity  of  the  color  is  not  always  an 
indication  as  to  the  quantity  of  organic  matter  or  oxide  of  iron 
present.  A  coarse  sand,  by  having  a  smaller  surface  to  be  colored, 
requires  much  less  coloring  material  than  a  clay  soil  which  has  a 
large  surface. 

1  Agr.  Science  i,  p.  251. 


PHYSICAL  PROPERTIES  OF  SOILS  113 

Specific  Gravity  of  Soils. — The  specific  gravity  of  a  body  is  the 
weight  of  the  body  divided  by  the  weight  of  an  equal  volume  of 
water.  Suppose  we  place  10  grams  of  soil  in  a  bottle  of  known 
weight  which  holds  exactly  25  cubic  centimeters,  and  weigh. 
Then  fill  the  bottle  exactly  full  of  water,  so  that  it  contains  no 
air,  and  weigh  again.  The  gain  in  weight  subtracted  from  the 
weight  of  25  cubic  centimeters  of  water  gives  the  weight  of  water 
displaced  by  10  grams  soil.  Ten  divided  by  this  gives  the  specific 
gravity  of  the  soil. 

In  estimating  the  specific  gravity  of  a  body,  we  must  allow  for 
the  space  occupied  by  air.  If  the  soil  could  be  fused  into  a  solid 
mass  without  chemical  change,  the  weight  of  i  cubic  centimeter 
expressed  in  grams  would  be  the  specific  gravity. 

The  specific  gravity  of  some  soil  materials  is  given  in  the 
following  table: 

SPECIFIC  GRAVITY  OF  SOIL  MATERIALS.       / 

/ 

Quartz 2.6  Water i.o 

Felspar 2.5-2.8  Humus 1.2-1.5 

Limestone  2.6-2.8  Mica 2.8-3.2 

Granite 2.6-2.7  Hornblende 2.9-3.4 

Clay 2.5  Talc 2.6-2.7 

SPECIFIC  GRAVITY  OF  SOILS. 

Clay  soil 2.65 

Sandy  soil 2. 67 

Fine  soil 2.71 

Humus  soil 2.53 

Apparent  Specific  Gravity. — The  apparent  specific  gravity  of 
a  soil  is  the  weight  of  a  given  volume  of  the  soil,  including  air 
spaces,  compared  with  the  weight  of  an  equal  volume  of  water. 

Apparent  specific  gravity  depends  upon  the  true  specific  gravity 
of  the  soil  particles,  and  the  amount  of  air  spaces  in  the  soil.  The 
former  is  constant,  the  latter  is  variable,  as  it  depends  upon  the 
size  and  shape  of  the  soil  particles  and  the  treatment  to  which  the 
soil  has  been  subjected.  A  cultivated  soil  contains  more  air 
spaces  than  the  same  soil  in  pasture. 

The  apparent  specific  gravity  will  vary,  then,  with  the  treat- 
ment to  which  the  soil  has  been  subjected,  if  it  is  determined  in 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


the  field.  In  the  laboratory  the  apparent  specific  gravity  will  vary 
with  the  method  used  for  determining  it. 

The  apparent  specific  gravity  of  a  soil  is  determined  by  weigh- 
ing the  dry  soil  that  occupies  a  given  volume.  In  the  field  this  is 
accomplished  by  driving  a  tube  of  definite  size,  not  less  than  2 
inches  in  diameter,  into  the  soil,  so  as  to  remove  a  core  of  known 
volume.  The  core  is  removed,  dried  and  weighed,  and  the  weight 
divided  by  the  volume  is  the  apparent  density. 

Apparent  density  is  determined  in  the  laboratory  by  packing 
200  to  1000  cc.  of  the  soil  into  a  glass  cylinder,  and  weighing  it. 
This  method  to  a  certain  extent  is  applicable  to  incoherent  soils, 
but  is  not  well  suited  to  clay  soils,  in  which  the  action  of  water 
has  a  decided  effect  upon  the  apparent  density.  It  represents  the 
weight  of  the  soil  when  in  condition  of  good  tilth. 

The  apparent  specific  gravities  of  different  kinds  of  soils  are 
as  follows,  according  to  Schubler  i1 


Apparent 
specific  gravity 

Weight  of 
dry  soil  per 
cubic  foot 

Weight  per  acre 
to  the  depth  of 
i  foot  in  pounds 

Sand 

T    7fi 

1.  /D 

I  28 

80  QO    " 

7(-    « 

o  o<yu<j>uiju 

Peat  

o  48—0  80 

/o 

•JO—  ^O        " 

ouou 

Sandy  soils,  usually  termed  "light,"  are  the  heaviest  of  all, 
while  clayey  land,  termed  "heavy"  weighs  less  than  ordinary  soils. 
The  terms  "light"  and  "heavy"  refer  to  the  readiness  with  which 
the  soils  are  worked  by  the  plow,  light  soils  requiring  much  less 
labor  than  heavy  ones. 

The  actual  weight  of  the  soil  in  the  field  varies  with  the  quantity 
of  water  present.  A  peaty  soil  saturated  with  water  is  very 
heavy. 

Since  soil  analyses  are  made  by  weight,  differences  in  the 
apparent  specific  gravity  of  soils  must  be  taken  into  consideration 
in  interpreting  the  results. 

1  Stockbridge,  Rocks  and  Soils,  p.  153. 


PHYSICAL  PROPERTIES  OF  SOILS 


The  apparent  specific  gravity  of  soils  taken  in  the  field  appears 
to  increase  as  we  go  downward.  This  is  in  part  due  to  the 
pressure  of  the  overlying  stratum ;  in  part  to  the  action  of  rain 
carrying  the  finest  particles  of  the  soil  into  the  open  spaces  of  the 
subsoil ;  in  part  to  the  loosening  action  of  tillage  and  plant  and 
animal  life  on  the  surface  soil  and  to  the  presence  of  their 
residues. 

The  weights  of  the  soil  per  acre  were  studied1  at  Rothamsted 
and  Woburn,  England,  by  driving  down  an  iron  frame  6  inches 
square  and  9  inches  deep.  The  core  of  soil  was  removed,  dried, 
and  weighed. 

WEIGHT  OF  SOIL  PER  ACRE. 


Pasture 
Rothamsted 

Arable  land 
Rothamsted 

Arable  land 
Woburn 

2  QOO  OOO 

3  200  ooo 

-I   A  oo  OOO 

Third.  Q  inches  •  

3  100  ooo 

-i  2OO  OOO 

3    TOO  OOO 

37OO  OOO 

3-7OO  000 

3   TOO  OOO 

The  Rothamsted  soil  is  a  heavy  loam  or  clay  subsoil  beneath 
which  is  the  chalk.  The  Woburn  soil  is  a  light  sand. 

Air  Space  in  Soils. — The  quantity  of  air  space  in  soils  may  be 
calculated  from  the  apparent  and  the  real  specific  gravity.  To 
say  that  the  soil  has  an  apparent  specific  gravity  of  1.20  means 
that  i  cc.  of  the  loose  soil  weighs  1.20  grams.  If  the  soil  material 
has  the  real  specific  gravity  of  2.5,  then  I  cc.  weighs  2.5  grams, 
and  i. 20  grams  of  it  occupies  1.20  divided  by  2.50  equals  0.48  cc. 
Thus  0.52  cc.  or  52  per  cent.,  is  air  space  in  this  particular 
instance. 

Adhesion  and  Cohesion. — Cohesion  is  the  force  with  which  the 
soil  particles  adhere  to  one  another.  It  varies  with  the  amount 
of  water  present  and  the  nature  of  the  soil,  from  zero  in  some 
sands,  to  a  high  degree  in  some  clays  when  dry.  Soils  with  little 
cohesion  when  dry  are  liable  to  be  blown  by  winds  unless  pro- 
tected by  vegetation.  The  larger  the  particles  of  soil,  the  less  is 

1  Warington,  Physical  Properties  of  Soil,  p.  46. 


Il6  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

the  cohesion  between  them.  When  the  particles  correspond  in 
size  to  silt,  the  wet  soil  may  be  a  sticky  mud,  like  clay,  and  is  often 
spoken  of  as  a  clay  soil,  but  when  dry  it  easily  falls  to  powder. 

The  behavior  of  soils  upon  drying  is  a  matter  of  great  practical 
importance.  Some  soils  in  drying  crumble  easily,  while  others 
form  clods  which  are  difficult  to  break  down.  This  behavior 
depends  to  a  certain  extent  upon  the  amount  of  water  present. 
Some  soils  crumble  easily  when  plowed  in  the  right  condition,  but 
when  too  much  water  is  present  they  form  intractable  clods. 

Cohesion  may  be  determined  in  the  dry  state,  or  the  wet  state. 
For  dry  cohesion,  the  soil  is  mixed  with  water,  molded  into  cakes 
of  uniform  size,  and  dried.  The  amount  of  force  required  to  crush 
the  cakes  is  then  determined.  This  throws  light  on  the  liability 
to  form  clods. 

For  moist  cohesion,  the  soil  is  mixed  with  water  to  50  per  cent, 
of  its  water  capacity,  and  the  power  required  to  separate  a  sec- 
tion of  the  soil  of  a  given  area  determined.  This  is  related  to 
the  plowing  of  the  soil. 

The  ease  or  difficulty  of  plowing  or  cultivating  a  given  field 
depends  largely  on  the  cohesion  of  the  soil.  A  measure  of  this  is 
the  draft  of  the  plow.  The  draft  of  a  plow  on  sandy  soil  may 
be  as  low  as  27  pounds  per  inch  in  depth  of  furrow,  as  against 
100  pounds  per  inch  for  clay.  This  means  that  the  former  would 
be  light  work  for  one  horse,  the  latter  heavy  work  for  three 
horses. 

Increasing  the  amount  of  organic  matter  in  the  soil  has  the 
effect  of  decreasing  the  cohesiveness  of  clays,  and  increasing  it 
for  sands.  A  dressing  of  lime  also  tends  to  decrease  cohesiveness 
of  a  soil. 

The  state  of  dryness  has  an  influence.  Sand,  lime,  and  humus 
have  little  adhesion  when  dry,  but  considerable  when  wet.  Clay, 
under  certain  conditions  of  moisture,  is  very  hard  to  plow.  The 
English  practice  of  burning  clays  overcomes  adhesion.  When 
clay  is  burned  and  then  crushed,  the  particles  no  longer  adhere 
tenaciously  when  wet,  and  the  mass  is  sandy-like  rather  than 
clayey. 


PHYSICAL  PROPERTIES  OF  SOILS  117 

Shrinking  on  Drying. — Some  soils  increase  in  bulk  when  they 
become  wet,  and  shrink  on  drying.  The  shrinkage  is  very  per- 
ceptible in  some  clay  soils.  They  become  full  of  cracks  and  rifts 
on  drying,  and,  since  they  harden  about  the  rootlets  imbedded  in 
them,  the  roots  may  become  ruptured  during  dry  weather.  Heavy 
clays  may  thus  lose  one-tenth  or  more  of  their  volume. 

Sand  does  not  change  in  bulk  on  wetting  or  drying,  and,  when 
present  to  a  considerable  extent  in  the  soil,  its  particles  prevent 
the  adhesion  of  the  clay  particles.  Although  a  loam  shrinks  on 
drying,  the  lines  of  separation  are  more  numerous  and  less  wide 
than  in  a  clay. 

Some  soils  crack  into  comparatively  small  masses  on  drying. 
These  are  often  termed  buckshot  soils.  Others  crack  into  larger 
masses,  several  feet  in  size.  In  others  irregular  cracks  are  found, 
sometimes  an  inch  in  width.  Schubler  prepared  cubes  of  various 
soil  constituents  and  determined  the  contraction  in  volume  on 
drying.  Pure  clay  contracted  18.3  per  cent,  of  its  volume;  humus 
from  the  center  of  a  decayed  tree  20  per  cent. ;  a  sandy  clay  6  per 
cent. ;  an  arable  soil  12  per  cent. ;  a  garden  soil  14.9  per  cent.  The 
rifts  allow  an  easier  drying  of  the  subsoil.  The  results  of  drying 
are  afterwards  favorable  in  a  clay  soil,  the  fissues  affording 
drainage  lines.  The  texture  is  improved,  drying  and  moistening 
being  favorable  to  formation  of  compound  particles.  Air  is  also 
admitted  to  the  subsoil,  and  oxidation  in  the  subsoil  is  promoted. 

Number  of  Particles  in  Different  Types  of  Soil. — These  have 
been  calculated  by  Whitney1  as  follows : 

Early  truck 1,955,000,000 

Truck  and  small  fruit 3,955,000,000 

Tobacco 6, 786,000,000 

Wheat 10, 228,000,000 

Grass  and  wheat 14,735,000,000 

Limestone 19,638,000,000 

The  basis  of  this  calculation  is  the  assumption  of  a  certain 

average  size  for  each  grade  of  soil  particle.     Knowing  the  size 

and  the  specific  gravity  of  the  soil,  the  weight  of  each  grade  of 

particle  can  easily  be  calculated.     Then  the  numbers  of  particles 

1  Bulletin  21,  Maryland  Station. 


Il8  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

of  each  size  can  be  calculated  from  the  weights  of  the  various 
separations  made  in  the  physical  analysis  of  the  soil. 

Relation  of  Fineness  to  Fertility. — The  state  of  division  of  a 
soil  has  some  effect  upon  its  fertility.  If  two  portions  of  a  rock 
are  prepared,  one  coarse,  and  the  other  finely  ground,  plants  will 
grow  better  on  the  latter.  With  the  same  material,  the  rapidity  of 
solution  is  in  direct  ratio  to  the  extent  of  surface  it  exposes.  The 
finer  the  particles,  the  more  abundantly  will  the  plant  be  supplied 
with  the  necessary  nourishment.  For  example,  a  cube  of  rock  I 
foot  square  has  6  sides  each  12  inches  square,  or  6  times  144 
square  inches  of  surface.  Cut  this  cube  into  cubes  of  I  inch 
square,  or  12  times  144  cubes,  each  of  which  has  six  sides,  one 
inch  square,  or  the  exposure  is  6  times  144  square  inches.  It  is 
easily  seen  that  as  the  division  increases,  the  surface  exposed  to 
the  action  of  roots  also  increases. 

It  must  not  be  assumed,  however,  that  finely  pulverized  sandy 
soils  would  yield  the  same  amount  of  plant  food  as  clay  soils. 
While  this  might  be  true  in  exceptional  cases,  as  a  rule  sandy 
soils  contain  less  plant  food,  as  may  be  shown  by  a  complete 
chemical  analysis  of  the  soil. 


CHAPTER  VII. 


THE  SOIL  AND  WATER. 

The  plant  food  is  dissolved  in  water  and  enters  the  plant 
through  its  roots.  Water  also  serves  as  the  medium  by  which 
matter  is  transferred,  and  it  supplies  the  hydrogen  and  a  part  of 
the  oxygen  used  in  the  synthesis  of  organic  matter. 

A  large  amount  of  water  is  required  by  plants,  not  only  because 
plants  contain  considerable  water,  but  also  because  the  passage  of 
water  through  plants  is  one  of  the  most  important  means  of  plant 
nutrition.  The  evaporation  of  water  from  the  surface  of  the 
leaves  produces  an  upward  current  of  water  which  carries  into 
the  plant  needed  mineral  material.  The  greater  the  evaporation, 
the  greater  is  the  transference  of  plant  food  from  the  soil  to  the 
plant,  other  things  being  equal. 

Transpiration. — The  loss  of  water  through  the  leaf  of  the 
plant  is  termed  transpiration.  The  amount  of  loss  by  transpira- 
tion is  easily  determined  with  plants  in  pots.1  We  weigh  the  pot 
of  soil  containing  the  plants  at  the  beginning  of  the  experiment 
and  at  the  end  of  certain  periods  weigh  it  again;  the  loss  of 
weight  plus  any  water  added,  is  water  evaporated  by  plant  and 
soil.  The  water  evaporated  from  a  pot  of  similar  soil  but  with 
no  plants,  under  the  same  conditions,  is  taken  to  show  the 
evaporation  from  the  soil  alone,  although  the  shade  of  the  plant 
make's  a  difference.  The  loss  of  water  by  soil  and  plants,  less  the 
loss  from  soil  alone,  gives  the  loss  by  the  plant  alone.  Correction 
must  be  made  for  the  increase  in  weight  of  the  plant,  if  the 
experiment  is  conducted  for  some  time.  In  another  form  of 
apparatus,  the  soil  is  covered  with  a  galvanized  iron  cover,  and 
the  openings  through  which  the  plant  extends  is  rendered  water- 
tight by  means  of  modelling  clay.  Plants  may  be  grown  in  the 
free  air  by  this  apparatus,  without  danger  of  irregular  results  due 
to  varying  amounts  of  rain  falling  in  different  pots  of  the  same 
series. 

If  the  plant  is  contained  in  pots  or  other  vessels  set  in  the 
1  Montgomery,  Proc.  Am.  Soc.  Agron.,  1911,  p.  257. 


I2O  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

ground,  or  if  it  is  too  large  to  be  weighed,  the  evaporation  of 
water  may  be  estimated  by  determining  the  quantity  of 
water  in  the  vessel  at  the  beginning  and  at  the  end  of  the  experi- 
ment (by  analysis  of  the  soil),  and  measuring  the  quantity  of 
water  received  by  the  vessel  during  the  course  of  the  experiment. 
In  the  transpiration  experiments  of  the  Bureau  of  Soils,  the 
plants  are  grown  in  wire  baskets  covered  with  paraffin.  Before 
the  measurements  of  transpiration  are  begun,  the  pot  is  sealed 
with  a  sheet  of  paper  coated  with  paraffin  so  as  to  exclude 
evaporation  as  much  as  possible,  a  suitable  hole  being  left  for  the 
plants.  The  pots  are  weighed,  and  the  loss  of  water  is  restored 
daily. 

Factors  of  Transpiration. — The  amount  of  water  transpired 
by  plants  depends  upon  several  factors : 

Humidity  of  Air. — Transpiration  decreases  as  the  humidity 
of  the  air  increases,  for  evaporation  into  dry  air  is  much  more 
rapid  than  into  moist  air.  At  the  Nebraska  Experiment  Station,1 
plants  were  grown  in  an  open  greenhouse,  in  which  the  air  was 
dry,  and  in  a  closed  greenhouse  in  which  floors  and  benches  were 
kept  wet,  and  water  atomized  into  the  air.  The  weights  of  water 
transpired  per  gram  of  dry  weight,  were  as  follows : 

In  dry  greenhouse 340 

In  moist  greenhouse 191 

Available  Water. — Plants  appear  to  transpire  more  as  the 
available  water  increases.  The  following  figures  show  the 
amounts  of  water  transpired  from  the  same  soil  containing  differ- 
ent quantities  of  water : 

Grams  water  used 

Per  cent,  saturation  per  grams  dry 

weight  produced 

IOO 290 

80 262 

60 239 

45 229 

35 252 

The  plants  grown  with  35  per  cent,  saturation  of  the  soil,  did 
not  grow  normally. 

1  Montgomery,  Proc.  Am.  Soc.  Agron.,  1911,  p.  276. 


THE  SOIL  AND  WATER 


121 


Light. — More  water  is  transpired  in  the  light  than  in  darkness. 
For  example,   Deherain1   determined  the   water  evaporated  per 
hour  and  100  grams  of  leaf,  to  be  as  follows: 
WATER  EVAPORATED. 


Wheat 

Barley 

Grains 

88.2 
17.8 
J.I 

Grams 

74-2 
18.2 

2.3 

On  the  other  hand,  excess  of  light  may  diminish  transpiration. 

Composition  of  the  Soil  or  Solution. — The  solution  brought  in 
contact  with  the  roots  or  stem  of  a  plant  exerts  a  decided  influence 
upon  the  amount  of  water  transpired.  According  to  Burger- 
stein,2  small  quantities  of  acid  added  to  distilled  water  increase 
transpiration,  alkalies  retard  it,  and  the  effects  of  salts  depend 
upon  the  nature  and  concentration  of  the  solution.  With  single 
salts,  transpiration  increases  with  the  concentration  of  the  solu- 
tion, until  a  maximum  is  reached.  The  effect  of  mixtures  of  two 
or  more  salts  depends  upon  the  nature  of  the  salts  used.  Of 
greater  agricultural  importance  is  the  fact  that  a  complete  nutri- 
tive solution  decreases  transpiration.  The  following  table  gives 
some  examples : 

The  fertility  and  nature  of  the  soil  also  appear  to  exert  an 


Salts 

Period 
(hours) 

Grams  water 
transpired  per  100 
grams  dry  matter 

With 
distilled 
water 

With  0.170 
per  cent, 
solution  of 
the  salts 
named 

Potassium 
Potassium 
Potassium 

94 
96 
120 

grams. 

1,838 
1,670 

2,794 

grams. 

1,142 
I,l6l 
i,939 

nitrate  and  magnesium  sulphate  •  •  • 

1  Jahresber.  f.  Agr.  Chem.,  1868,  p.  273 
*  Jahresber.  f.  Agr.  Chem.,  1875,  p.  388. 
9 


122 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


influence  upon  the  quantity  of  water  transpired.  Widstoe1  found 
that  the  transpiration  of  corn  is  from  552  per  gram  dry  matter 
on  a  loam,  to  1616  on  a  sand  or  clay. 


Fig.  32. — Pot  experiments,  on  moisture  used  by  plants.  Utah  Station. 
Demoussy,  at  the  Grignon  Experiment  Station,  found  that  the 
poorer  the  soil,  the  more  water  was  transpired.     The  following 
figures  are  quoted  from  him. 
GRAMS  OF  WATER  TRANSPIRED  PER  i  GRAM  DRY  MATTER  PRODUCED. 


Rye  grass 

Clovers 

630 
233 
435 
449 
630 

454 
398 
255 
272 
322 

1  Utah  Bulletin,  No.  105. 

2  Not  manured  the  same  as  the  rye  grass. 


THE  SOIL  AND  WATER  123 

In  some  pot  experiments  of  Konig,  similar  results  were  secured. 
The  relative  quantity  of  crop  he  produced  on  three  soils  was 
100:122:134,  while  the  relative  transpiration  of  water  was 
100 :  74 :  63,  being  in  the  opposite  direction.  Gardner1  found  in 
wire  basket  experiments,  that  as  fertilizers  increase  plant  growth, 
there  is  a  marked  diminution  in  water  transpired  per  unit  of 
growth. 

It  would  appear  that  a  fertile  soil  conserves  moisture,  so  far  as 
transpiration  is  concerned,  much  better  than  a  poor  one.  That 
is  to  say,  the  better  supplied  a  soil  is  with  plant  food,  the  larger 
is  the  crop  which  it  can  produce  with  a  limited  supply  of  water. 
The  presence  of  plant  food  results  in  an  economy  of  water.  The 
smaller  the  quantity  of  available  plant  food  present,  the  greater 
seems  to  be  the  effort  made  by  the  plant  to  secure  sufficient  plant 
food,  by  increasing  the  current  of  water  passing  through  it. 

Results  of  an  experiment  with  corn  on  soil  types  at  the 
Nebraska2  Experiment  Station,  are  as  follows : 


Character  of  soil 

Water  transpired  per  gram 

Unmanured 

Manured 

"Very  poor  (15  bu  )  

540 
478 
391 

350 
34J 
346 

Intermediate  (  ^o  bu  )  

Quite  fertile  (50  bu  )  

Variety  of  Plant. — The  difference  in  the  transpiration  of  differ- 
ent kinds  of  plants  is  probably  a  factor  in  the  adaptability  of 
plants  to  climate  and  soils.  Plants  which  live  in  dry  regions, 
such  as  cactus,  salt  bush,  etc.,  transpire  less  water  than  plants 
adapted  to  moist  sections.  There  are  other  causes  of  endurance 
of  drought,  however,  such  as  the  deeper  rooting  already  dis- 
cussed. 

According  to  Fittbogen  there  is  no  relation  between  transpira- 
tion and  the  production  of  organic  substance,  as  measured  by  the 
carbon  dioxide  decomposed. 

1  Bureau  of  Soils,  Bull.  48. 

2  Proc.  Am.  Soc.  Agri.,  1911,  p.  277. 


124 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Amount  of  Water  Required  by  Plants. — The  amount  of  water 
transpired  during  the  growth  of  a  plant  may  be  calculated  as  parts 
of  water  per  one  part  of  dry  matter  of  the  plant,  and  may  be 
considered  to  represent  the  amount  of  water  required  by  the 
plant.  This  quantity  will  vary  considerably  according  to  the  con- 
ditions surrounding  the  plant,  as  we  have  seen  in  the  preceding 
paragraphs.  An  estimate  of  the  amount  of  water  required  to 
produce  a  given  weight  of  dry  matter  is,  therefore,  only  approxi- 
mate. Such  an  estimate  may,  however,  aid  in  the  consideration 
of  problems  relating  to  the  water  content  of  the  soil.  The  figures 
given  in  the  table  were  secured  in  experiments  of  four 
investigators.1 

POUNDS  OF  WATER  EVAPORATED  BY  THE  PI,ANT  PER  POUND  OF 
DRY  MATTER  PRODUCED. 


Lawes 
and  Gilbert 

Hellriegel 

King 

Wollny 

Barley  

262 

•y  TO 

•JQ7 

*, 
262 

obO 

214 

fi/lfi 

O/1 

Clover  (red)  •  • 

*/« 

233 

•*4y 

6ou 

4oo 

Millet  

o/o 

416 

Mustard  

SAI 

Oats  

4O2 

c  C7 

66  c 

ppac 

w*»0 

Potatoes 

•*oo 

292 

4// 

447 

Rape 

4-^0 

Rve 

912 

xv_yc   •  • 

oil 

Wheat  

22^ 

q.yu 

•"0 

OOV 

In  some  of  the  arid  states  of  the  United  States,  fair  crops  of 
wheat  are  grown  with  an  annual  rainfall  of  13  to  18  inches,  most 
of  which  falls  in  the  winter  before  the  growing  period  of  the  crop 
begins.  This  small  quantity  of  water  is  effective,  partly  because 
the  soils  are  rich  in  soluble  plant  food,  partly  because  the  saline 
matter  in  solution  decreases  transpiration. 

1  Exp.  Sta.  Record  4,  532,  Rep.  Wis.  Station,  1894;  Jour.  Hort.  Soc. 
Eng. ,  1850.  See  also  Widstoe,  Utah  Bui.  No.  105  ;  Montgomery,  Proc.  Am. 
Soc.  Agri.,  1911,  p.  261. 


THE)  SOIL  AND  WATER 


125 


In  regions  of  deficient  rainfall,  the  crop  produced  is,  as  a  rule, 
somewhat  proportional  to  the  water  supply.  S.  Fortier1  in 
Montana  made  experiments  with  wheat  grown  in  tanks.  The 
crop  secured  increased  quite  regularly  with  the  amount  of  water 


I 


pig  33.— Relation  of  rainfall  for  June,  July  and  August  to  yield 
of  corn  per  acre.     U.  S.  D.  A. 

supplied.  In  California,  he  found  that  the  natural  rainfall,  4^ 
inches  during  the  growth  of  the  wheat,  produced  straw,  hut  no 
grain ;  four  inches  of  irrigation  water  produced  at  the  rate  of  10 
bushels,  and  sixteen  inches  of  water  increased  the  yield  to  thirty- 
eight  bushels  per  acre.  Even  in  humid  climates,  irrigation  may 
result  in  largely  increased  yields.2  King3  in  Wisconsin  grew 
crops  in  barrels  sunk  level  with  the  ground  surrounded  by  the 
same  crop  as  was  in  the  barrel.  The  soil  was  kept  saturated  with 
water  six  inches  above  the  bottom  of  the  barrel.  The  crops  pro- 
duced far  exceeded  those  produced  in  the  surrounding  field. 
The  water  used  equaled  24  inches.  The  yield  of  oats  and  barley 

1  Rep.  Montana  Exp.  Sta.,  192-3. 

2  King,  Farmers'  Bulletin  No.  46. 

3  Rep.  Wis.  Exp.  Sta.,  1893. 


126 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


was  10,000  pounds  dry  matter  per  acre.     The  abundant  supply 
of  water  thus  had  a  striking  effect. 

Smith1  has  studied  the  relation  of  the  rainfall  to  the  yield  of 
corn.  Figure  33  shows  the  relation  between  the  average  yield  of 
corn  in  bushels  per  acre,  and  the  rainfall,  in  Ohio,  Illinois,  Indiana, 
Iowa,  Nebraska,  Kansas,  Missouri,  and  Kentucky  for  the  years 
1 883  to  1902  inclusive. 

Duty  of  Water. — Duty  of  water  is  a  term  applied  by  irrigators  as 
the  measure  of  the  quantity  of  water  used  per  acre,  but  the  term  is 
also  applied  to  the  service  which  water  may  render  in  producing 
crops.  McGee2  estimates  that  it  requires  approximately  1,000 
pounds  of  water  during  the  year  to  produce  one  pound  of  grains, 
etc.  This  estimate  allows  for  losses  by  evaporation,  and  its  basis 
is  the  aggregate  yearly  supply  of  water  from  all  sources  He 
presents  the  following  table,  based  on  personal  observation,  show- 
ing estimates  of  crop  yields  with  varying  amounts  of  water  for 
the  entire  year : 


Depth  per  acre 

Corn 

Oats 

Wheat 

1  8  inches  •                   .... 

bushels 

IO 

bushels 

T  r 

bushels 
5 

^6  inches  ••        

•7  C 

xo 
An 

12 

48  inches  

6j 

7O 

80 

2c 

/w 
TOC 

1  2O 

*3 

A.O 

1WO 

These  figures,  are  roughly  approximate,  as  there  are  great 
variations  in  conditions.  According  to  this  table,  36  inches  yearly 
rainfall  will  produce,  on  an  average,  35  bushels  of  corn. 

Quantity  of  Water  in  Soil. — The  following  figures  of  Hellriegel3 
are  the  result  of  an  experiment  to  ascertain  the  effect  of  the 
amount  of  water  in  the  soil  upon  the  crop  production.  The 
experiment  was  carried  out  in  pots. 

1  Yearbook,  U.  S.  Dept.  Agr.,  1903,  p.  216. 

2  Yearbook,  U.  S.  Dept.  Agr.,  1910,  p.  174. 

3  Jahresber,  f.  Agr.  Chem.,  1870-2,  p.  161. 


THE  SOIL  AND  WATER 
EFFECT  OF  MOISTURE  ON  CROP. 


127 


Moisture  in  percentage  water  capacity  of  the  sand 

Barley 

,  Total 

Grain 

80  

19.69 
22.76 
21.76 
17.19 
14.62 
6.30 
0.12 

8.77 
9.96 
10.51 
8.70 

7-75 
0.72 

60  

6^  '  ' 

jO  ... 

The  most  favorable  quantity  of  water  in  this  case  was  40  per 
cent,  of  the  water  capacity  of  the  sand.  Necessarily  in  this 
respect  there  will  be  a  difference  for  different  kinds  of  plants. 

According  to  this  experiment,  there  is  an  optimum  condition 
of  the  soil  at  which  the  moisture  content  is  most  favorable  to 
plant  growth.  Below  or  above  this  optimum,  there  is  a  decrease 
in  yield,  independent  of  the  wilting  of  the  plant.  Wilting  is  a 
sign  of  distress,  signifying  that  moisture  is  lacking  to  an  extent 
that  endangers  the  life  of  the  plant.  The  growth  may  suffer 
from  lack  of  water  long  before  wilting  takes  place.  The  experi- 
ments of  Hellriegel  were  carried  on  in  pots,  in  which  there  was  a 
limited  amount  of  soil  at  the  disposal  of  the  plants.  In  the  open 
field,  in  which  a  greater  range  of  root  development  is  permitted,  a 
smaller  percentage  of  available  water  may  suffice. 

Forms  of  Water  in  the  Soil. — Water  is  present  in  the  soil  as 
water  of  hydration,  hygroscopic  water,  capillary  water,  and  flow- 
ing water. 

Water  of  hydration  is  water  in  chemical  combination  with  cer- 
tain soil  constituents,  such  as  hydrated  silicates  (zeolites)  and 
hydrated  oxide  of  iron.  Most  of  it  is  retained  when  the  soil  is 
dried  at  100°,  and  is  driven  off  on  heating  the  soil  to  a  high  tem- 
perature. As  water  of  hydration  cannot  be  taken  up  by  plants,  it 
cannot  be  considered  to  be  of  value  to  the  plant. 

Hygroscopic  Water  is  water  which  is  absorbed  by  the  soil  from 
the  atmosphere.  Every  body  in  a  moist  atmosphere  has  a  layer  of 
water  upon  it,  the  thickness  of  which  depends  upon  the  tempera- 


128  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

ture  and  the  degree  of  saturation  of  the  atmosphere.  The 
capacity  of  the  soil  to  hold  hygroscopic  water  can  be  determined 
by  placing  a  thin  layer  of  soil  in  a  vessel,  the  air  of  which  is 
saturated  with*  water ;  the  soil  will  take  up  a  certain  amount  of 
water,  which  can  be  determined  by  the  gain  in  weight  of  the  soil. 
The  temperature  of  the  containing  vessel  must  be  uniform,  for 
variations  in  temperature  in  a  saturated  atmosphere  will  be  liable 
to  form  dew  on  the  soil.  The  layer  of  soil  must  be  very  thin,  not 
over  one  millimeter  thick.  This  method  gives  the  maximum 
hygroscopic  capacity ;  if  the  air  is  not  fully  saturated,  lower 
results  will  be  obtained. 

The  amount  of  hygroscopic  water  taken  up  depends  very 
largely  on  the  character  of  the  soil.  According  to  Hilgard  and 
Loughridge,1  soils  absorb  the  following  amounts  of  hygroscopic 
moisture : 

Hygroscopic  moisture 
Per  cent. 

Sandy  soils  (less  than  5  per  cent,  clay) 3 

Sandy  loams 3-5 

Loams 5 

Clay  loams 5-7 

Clay 7-10 

The  amount  of  hygroscopic  water  taken  up  by  a  given  sub- 
stance depends  partly  upon  its  surface  area.  A  mass  of  quartz 
will  absorb  much  more  moisture  when  in  fine  powder  than  when 
in  large  fragments.  It  is  also  greatly  influenced  by  the  amount 
and  character  of  the  colloid  constituents  in  the  soil,  such  as 
hydrated  ferric  oxide,  alumina,  gelatinous  silica,  hydrated  silicates, 
and  especially  humus.  Pure  clay  has  a  somewhat  lower  absorp- 
tive power  than  these. 

Value  of  Hygroscopic  Moisture. — Plants  are  not  able  to  utilize 
the  hygroscopic  moisture  of  soils.  At  least,  they  wilt  before  the 
moisture  in  the  soil  is  withdrawn  to  the  amount  held  by 
hygroscopic  power. 

Heinrich2  grew  plants  in  very  small  boxes  until  well  developed 

1  Rep.  Cal.  Exp.  Sta.,  1897-8. 

2  Jahresber,  f.  Agr.  Chem.,  1875-6,  p.  368. 


THE:  soiiv  AND  WATER 


129 


and  then  placed  them  under  conditions  of  very  little  evaporation 
until  they  began  to  wilt.  The  moisture  in  the  soil  was  then 
determined.  The  hygroscopic  moisture  was  also  determined  by 
the  method  already  indicated.  A  variety  of  soils  and  plants  were 
used.  The  following  table  shows  the  average  results  secured  with 
Indian  corn  and  oats  : 


Water  per  100  of  dry  soil 

When  plants 
wilted 

Hygroscopic 
water 

1-5 

4.6 

6.2 

7.8 
9.8 
49-7 

1.2 

3-° 
4.0 

5-7 
5-2 
42.3 

Calcareous  soil  

pAOf 

It  appears  that  hygroscopic  water  may  be  of  advantage  in 
regions  of  hot,  dry  winds ;  the  higher  the  hygroscopic  water,  the 
less  rapidly  the  soil  dries  out  and  heats  up.  It  also  appears  that 
heavy  fogs,  such  as  occur  in  parts  of  California,  may  add  to  the 
hygroscopic  water  of  the  soil,  and  keep  the  plant  growing  slowly 
when  rainfall  is  lacking. 

Capillary  Moisture. — This  is  the  thin  film  of  water  surround- 
ing the  soil  particles  and  so  held  between  them  that  it  cannot  flow 
off.  In  a  clean  glass  tube  of  i  mm.  internal  diameter,  capillary 
attraction  will  cause  water  to  rise  15.3  cm;  if  the  bore  is  o.i  mm. 
the  water  will  rise  153.6  cm;  if  it  is  o.oi  mm.  the  water  will 
rise  1536.6  cm.  That  is,  the  height  to  which  the  water  is  carried 
varies  inversely  as  the  diameter  of  the  tube.  It  also  varies  with 
the  temperature  and  the  liquid  used. 

If  glass  tubes  be  filled  with  various  soils  and  the  lower  ends  of 
these  be  set  in  water,  a  great  difference  will  be  observed,  both  in 
the  speed  and  in  the  height  to  which  the  water  rises  in  them.  This 
is  the  method  used  for  comparing  the  capillarity  of  dried  soils. 

The  following  table1  exhibits  the  differences  in  the  height  to 
which  water  rises  in  some  soils : 

1  Meister,  Jahresber.  f.  Agr.  Chem.,  1859-60,  p.  42. 


130 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


5J£  hours 

•2\Yz  hours 

inches 

44 
44 
38 
37 
26 

21 

inches 

80 
70 
64 
45 
36 
28 

Quartz  sand  

Briggs  and  Lapham1  found  that  water  rose  37.5  cm.  in  a  dry 
soil,  while  in  a  moist  soil  it  rose  over  165  cm.  The  method  of 
work  was  as  follows : 

Two  tubes  of  glass  were  provided  with  perforated  bases,  filled 
with  soil,  and  saturated  with  water  by  sucking  it  up  through  the 
earth.  One  tube  was  then  sealed  at  the  base,  and  the  other 
inserted  into  a  reservoir  of  water.  At  various  intervals  of  time, 
both  tubes  were  weighed.  If 'water  rises  by  capillary  action,  the 
tube  with  reservoir  attached  will  lose  water  more  rapidly  than 
the  other  one.  If  not,  a  section  of  the  tube  was  removed  after  a 
suitable  interval,  and  the  operation  repeated.  For  example,  with 
one  soil,  no  loss  occurred  at  180  cm. ;  loss  occurred  at  165  cm. 
The  capillary  water  rose  165  cm.,  but  did  not  rise  180  cm. 

The  so-called  capillary  moisture  of  the  soil  is  held  as  thin  films 
of  water  surrounding  the  soil  particles,  due  to  what  is  called  "sur- 
face tension."  The  surface  of  the  film  of  water  surrounding  the 
soil  particle  is  in  the  condition  of  an  elastic  membrane  exerting 
considerable  pressure  and  consequently  holding  the  water  firmly 
against  the  soil  particle.  In  a  fully  drained  soil  there  is  a  condition 
of  equilibrium  between  the  force  of  surface  tension  and  the  force 
of  gravity.  If  the  film  of  water  becomes  thicker  and  heavier,  the 
force  of  gravity  will  gradually  draw  away  the  excess  of  water. 
If  the  films  become  thinner,  a  force  is  developed  which  may  cause 
a  flow  of  water  from  thicker  neighboring  films. 

Loughridge2  studied  the  capillary  action  of  soils  placed  in 
copper  tubes  one  inch  in  diameter  and  in  one  foot  lengths,  fitting 

1  Bulletin  19,  Bureau  of  Soils. 

2  Rep.  Cal.  Exp.  Sta.,  1892-4 


THE;  SOIL  AND  WATER  131 

into  each  other.  One  side  of  the  tube  was  made  of  glass  so  that 
the  contents  might  be  observed.  The  bottom  tube  was  closed  at 
its  lower  end  with  muslin  and  the  tubes  filled  with  air-dry  soil, 
stirred  in  with  a  wire  and  made  firm  by  a  slight  tapping  on  the 
table.  In  experiments  with  a  sandy  soil,  an  alluvial  soil,  a  silty 
soil,  and  an  adobe  soil,  water  rose  rapidly  in  the  two  coarser  soils, 
reaching  8  to  9  inches  in  the  first  hour,  while  the  water  in  the 
stiff  soil  rose  only  i  to  2  inches.  The  water  rose  rapidly  in  the 
sand,  but  only  reached  a  final  height  of  i6*/2  inches.  The  other 
three  soils,  in  125  or  195  days,  reached  nearly  the  same  height, 
but  the  alluvial  soil,  composed  mostly  of  fine  sand  and  silt,  carried 
the  water  up  most  rapidly.  This  experiment  is  an  instructive 
illustration  of  the  difference  in  the  capillary  powers  of  soils. 

Water  thus  tends  to  distribute  itself  in  the  soil,  through 
capillary  passages  or  by  the  slower  processes  of  surface  distribu- 
tion. When  these  operations  are  assisted  by  gravitation,  as  when 
rain  falls,  the  water  moves  rapidly.  When  the  movement  of 
water  is  opposed  by  gravitation,  as  when  a  soil  dries  at  the  sur- 
face and  is  wet  below,  the  movement  is  retarded  by  the  increasing 
height  of  the  column  of  water  lifted,  until  finally  it  entirely 
ceases. 

Capillary  action  has  some  effect  in  raising  water  from  the 
water  table  in  a  few  instances  when  the  water  table  is  less  than 
about  four  feet  from  the  surface.  One  great  function  of  capillary 
action  and  surface  tension  is  to  distribute  water  to  the  roots. 
When  water  is  withdrawn  at  one  place  by  the  roots,  it  disturbs  the 
equilibrium  and  causes  a  flow  of  water  from  points  of  least 
resistance. 

Flowing  Moisture. — Water  present  in  excess  of  the  hygroscopic 
moisture  held  by  capillary  action,  may  be  termed  flowing  water. 
It  will  pass  downward  through  the  soil  at  a  rate  depending  upon 
the  permeability  of  the  soil. 

The  quantity  of  water  in  a  saturated  soil  depends  entirely  upon 
the  air  space  in  the  soil.  The  soil  is  saturated  when  all  the  air 
space  is  filled  with  water.  The  air  space  can  be  calculated  from 
the  real  and  the  apparent  specific  gravity  of  the  soil. 


132 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Sand  and  gravel  separately  have  an  air  space  corresponding  to 
about  40  per  cent,  of  their  total  volume.  When  mixed  together, 
the  small  particles  of  sand  enter  the  free  space  of  the  gravel,  and 
diminish  the  volume  of  the  free  space.  In  ordinary  soils,  the  vol- 
ume of  the  free  space  is  somewhat  greater  than  in  sand  or  gravel, 
owing  to  the  presence  of  porous  or  compound  particles. 
A  soil  abounding  in  porous  compound  particles  decreases  in  water 
capacity  when  reduced  to  a  powder.  Zenger  found  that  the  soil 
from  a  peaty  meadow  held  178  parts  water  to  100  parts  soil, 
but  it  held  only  103  parts  water  when  finely  powdered.  Colloidal 
bodies  take  up  water  and  make  the  soil  swell  when  wet. 

A  soil  is  seldom  completely  saturated  under  natural  conditions. 
The  soil  cannot  become  fully  saturated  unless  the  air  which  fills 
the  interstices  of  the  soil  is  allowed  to  escape.  Rain  covers  the 
surface  of  the  soil  and  closes  the  path  of  the  air  so  that  it  gets 
out  with  difficulty.  Only  after  long  continued  rains  do  soils  be- 
come nearly  saturated. 

The  following  table  shows  the  quantity  of  water  in  naturally 
saturated  soils,  the  samples  being  collected  after  continued  rains : 


• 

Water  in  naturally  saturated  soils 

Parts  per 
100  of  wet  soil 

Parts  per 
100  of  dry  soil 

18.4 
22.4 

24.1 

25-7 
23.0 
24.7 

37-6 

22.5 
28.9 
31-8 
34-7 
29.9 
32-8 
60.2 

Clay  loam  

L/oani   artificial  manure  26  years  

The  first  four  analyses  were  made  by  King.1  The  last 
three  samples,  from  the  Rothamsted2  Experimental  fields, 
show  the  effect  of  humus  upon  the  water  capacity.  The 
accumulation  of  humus  in  the  soil  manured  with  barnyard  manure 
increases  the  water  capacity  of  the  soil  decidedly.  On  account 

1  Wisconsin  Report,  1890. 

'2  Jour.  Roy.  Agr.  Soc.,  1871,  p.  no. 


THE;  sou,  AND  WATER 


133 


of  the  larger  amount  of  stubble  left  by  the  crop  produced  with  a 
complete  mineral  fertilizer,  this  soil  also  holds  more  water  than 
the  one  with  no  manure. 

Method  of  Expressing  Water  in  Soils. — The  amount  of  water 
contained  in  a  soil  may  be  expressed  in  three  ways1;  first,  in 
terms  of  the  volume  of  water  which  occupies  a  given  volume  of 
soil ;  second,  in  percentage  of  water  contained  in  the  wet  soil ; 
third,  in  percentage  of  the  dry  soil.  The  following  table  (after 
Warington)  gives  the  water  in  some  soils  fully  saturated: 


Water  in  saturated  soils 

Volume  of 
water  per  100 
volume  of  soil 

Water  by  weight 

In  100 
of  wet  soil 

Per  100 
of  dry  soil 

39-4 

45-4 
49-5 
50.0 
60.1 
69.0 
84.0 

19.8 

23.3 
28.2 
27.8 
31.2 

43-4 
78.2 

24.7 
30-4 
39-2 
38.5 
45-4 
76.8 
259.0 

Chalk  soil  

Olflv 

^iay  

It  is  better  to  compare  volumes  of  water  in  given  volumes  of 
soil  in  considering  the  water  content  of  different  soils.  The  roots 
of  the  plant  are  distributed  through  a  given  space,  which  varies 
according  to  the  kind  of  plant,  depth  of  soil,  etc.,  and  it  is  the 
quantity  of  water  and  plant  food  in  the  space  occupied  by  the 
roots  which  is  important.  This  method  of  expression  is,  how- 
ever, cumbersome;  for,  in  addition  to  the  weight  of  soil  and  weight 
of  water,  there  must  enter  into  the  calculation  the  real  and  appar- 
ent specific  gravity  of  the  soil. 

The  expression  of  the  water  absorbed  in  terms  of  the  weight  of 
the  dry  soil  has  decided  advantages,  especially  in  laboratory  work. 
Only  two  quantities  are  involved,  the  weight  of  the  soil  and  the 
weight  of  the  water.  It  is  thus  easy  to  calculate  the  amount  of 
water  which  should  be  present  in  a  given  weight  of  soil  to  produce 
a  definite  degree  of  saturation. 

1  Warington,  Physical  Properties  of  Soils,  p.  69. 


134  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Expressing  the  water  present  by  weight  in  100  parts  of  dry  soil 
exaggerates  the  differences  between  soils.  This  is  most  marked 
when  peat  is  compared  with  a  sand,  for  we  really  compare  the 
water  in  seven  volumes  of  wet  peat  with  one  volume  of  wet  sand. 

Retention  of  Water  by  the  Soil. — A  soil,  though  protected  from 
evaporation,  does  not  remain  fully  saturated,  but  loses  water 
through  capillary  action  and  the  action  of  gravity.  If  a  wide 
tube  of  sufficient  length,  filled  with  coarse  sand  of  uniform  sized 
particles,  is  saturated  with  water  and  allowed  to  drain,  we  find 
two  distinct  layers;  a  short  column  of  sand  fully  saturated, 
and  a  long  column  above  it  fully  drained,  and  containing  a  nearly 
uniform  quantity  of  water. 

If  the  particles  of  sand  are  not  uniform  in  size,  as  in  an 
ordinary  soil,  then  we  find  three  layers,  but  not  sharply  distinct  as 
in  the  preceding  case.  The  highest  layer  is  fully  drained,  and 
the  content  of  water  of  the  soil  increases,  until  the  lowest  layer 
is  fully  saturated.  The  water  in  the  fully  drained  layer  not  only 
coats  the  particles  but  fills  the  finest  of  the  interspaces.  The  pro- 
portion of  interspaces  occupied  by  water  increases  toward  the 
bottom  of  the  tube,  until  finally  all  the  interspaces  are  filled  and 
the  soil  is  saturated. 

The  following  experiment  of  King1  exhibits  the  differences 
between  two  classes  of  soil  material.  Tubes  10  feet  long  and  6 
inches  in  diameter  were  filled  with  sand  prepared  by  sifting 
through  sieves  of  different  degrees  of  fineness.  The  sand  was 
saturated  with  water,  and  allowed  to  drain,  protected  perfectly 
from  evaporation,  for  in  days.  The  water  in  each  6  inches  of 
the  columns  was  then  determined.  Two  of  the  series  are  shown 
in  the  table . 

The  particles  in  tube  I  are  nearly  uniform ;  the  water  content 
is  nearly  constant  until  the  ninth  foot  is  reached,  when  it  suddenly 
increases.  The  particles  in  tube  II  are  of  varying  size;  the  water 
content  increases  constantly  from  the  top  to  the  bottom. 

The  amount  of  water  retained  by  a  drained  soil  depends  upon 
the  smallness  of  the  spaces  between  the  particles,  and  also  on 
1  Report  Wisconsin  Station,  1893. 


THE:  SOIL  AND  WATER 


whether  or  not  the  particles  are  porous.  The  smaller  the  particles 
and  the  more  porous  they  are,  the  greater  the  quantity  of  water 
held.  Humus  and  other  organic  matter,  being  porous,  increase 
the  water  retained  considerably. 


i 
Particles 
1/60"  to  1/80" 

ii 

Particles 
less  than  i/ioo" 

Per  cent. 

2.40 
2.72 
2.79 

2.93 
2.98 
3.12 
3-H 
3-54 
I3-50 
20.51 

Per  cent. 

3-35 
3-53 
4-03 
5-i6 
6.99 

9.83 
10.98 
15.88 
18.90 
19.99 

Third  foot  

Fifth   font 

'viirtVi   foot 

SpvfMit  H  foot 

Eighth,  foot          •            •                     ' 

Ninth  foot  •  •      •          •     •  •        ....              

Tenth  foot  

The  water  held  by  drained  soils  may  be  determined  by  placing 
the  soil  in  tubes  which  can  be  divided  into  sections,  as  in  the  ex- 
periment of  King  cited,  though  the  tubes  need  not  be  so  large. 
After  the  soil  has  been  saturated  and  is  fully  drained,  the  water  is 
determined  in  the  different  sections.  Unless  the  tube  is  sufficiently 
long,  the  upper  sections  will  not  be  fully  drained.  The  length  of 
tube  required  depends  upon  the  character  of  the  soil.  The  follow- 
ing figures  of  Schloesing  show  the  quantity  of  water  held  by  fully 
drained  soils : 

Weight  of  water  in 
100  parts  of  drained  soil 

Coarse  sand 3.00 

Fine  sand 7.30 

Calcareous  sand 32.00 

Clay  soil 35-oo 

Forest  soil 42.00 

The  state  of  consolidation  of  soil  affects  the  water  held  by  it. 
Closely  packed  particles  will  retain  at  least  twice  as  much  water 
per  unit  of  volume  as  particles  loosely  packed.  Sandy  soil  has  its 
capacity  increased  by  rolling,  and  that  of  clay  soil  is  reduced  by 
pulverization. 


136  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Water  Capacity. — The  water  capacity  of  a  soil  is  the  amount 
of  water  held  by  the  partly  drained  soil.  Fifty  grams  of  soil 
are  placed  in  a  tube  i%  inches  in  diameter,  allowed  to  drain,  and 
weighed.  The  gain  in  weight,  expressed  in  per  cent.,  is  the  water 
capacity.  Other  methods  which  vary  in  detail  are  used.  The 
percentage  of  water  held  will  vary  with  the  height  of  the  column 
of  soil,  and  to  some  extent,  with  the  time  of  draining,  but  the 
results  are  comparable  if  the  same  method  is  used  on  different 
soils. 

The  following  figures  show  the  water  capacity  of  some  types 
of  soils,  determined  by  the  method  given  above : 

Water  capacity 

of  some  soils1 

Per  cent. 

Tarboro  sand • 25. i 

Norfolk  sand  29 .6 

Cecil  clay 45.0 

Cecil  sandy  loam 36.8 

Durham  sandy  loam 28.9 

Amount  of  Water  at  Disposal  of  Plant. — The  amount  of  water 
at  the  disposal  of  the  plant  varies  from  time  to  time,  according  to 
a  number  of  factors.  The  principal  groups  of  factors  are  as 
follows:  (i)  The  available  water  in  the  soil;  (2)  the  root  area  of 
the  plant;  (3)  the  losses  and  gains  of  water  by  the  soil;  (4)  the 
depth  of  the  water-table. 

Available  Water  in  the  Soil. — The  amount  of  available  water 
in  the  soil  depends  upon  the  nature  of  the  soil,  and  the  nature  of 
the  plant. 

Nature  of  Soil. — The  forces  which  cause  water  to  enter  a  plant 
are  opposed  by  the  osmotic  pressure  of  the  soil  solutions  and  by  the 
hygroscopic  attraction  of  the  soil  particles  for  water.  The  soil 
attraction  increases  as  its  moisture  content  diminishes,  con- 
sequently decreasing  the  rate  of  entrance  into  the  plant,  and 
diminishing  the  production  of  organic  substance  if  the  amount 
supplied  is  below  the  optimum.  When  the  outgo  of  water 
becomes  greater  than  the  income,  the  plant  wilts.  The  point  at 
which  wilting  takes  place  varies  with  the  nature  of  the  plant,  but 
1  Rep.  N.  C.  Exp.  Sta.,  1902-3,  p.  39. 


THE:  SOIL  AND  WATKR  137 

depends  also  on  the  nature  of  the  soil,  the  temperature,  and  the 
humidity  of  the  air. 

Briggs1  and  associates  have  elaborated  methods  for  the  deter- 
mination of  the  wilting  point  of  plants,  and  traced  the  relation 
between  the  moisture  content  of  the  soils  at  the  time  of  wilting, 
and  the  moisture  equivalents  of  the  soils,  their  hygroscopic  power 
and  their  capacity  to  hold  moisture.  The  moisture  equivalent  is 
the  percentage  of  moisture  the  soil  will  retain  in  opposition  to  a 
centrifugal  force  1,000  times  the  force  of  gravity.  The  relations 
between  these  factors  he  expresses  as  follows : 

moisture  equivalent 
Wilting  coefficient  —  - 

i  .84 

hygroscopic  co-efficient 

0.68 

moisture-holding  capacity  —  21 
2.90 

The  water  which  cannot  be  withdrawn  from  soils  by  a  plant 
may  be  termed  unavailable  water,  and  that  in  excess  of  this, 
available  water.  The  California  Experiment  Station  holds  the 
available  water  to  be  practically  the  hygroscopic  water,  that  is, 
the  moisture  absorbed  from  the  soil  by  a  damp  atmosphere. 

Nature  of  the  Plant. — Plants  vary  in  their  power  of  absorbing 
water  from  soils.  That  is  to  say,  some  plants  will  reduce  the 
water  in  the  same  soil  to  a  lower  percentage  than  others,  before 
wilting.  This  may  be  due  in  part  to  difference  in  the  ratios  be- 
tween root  area  and  surface  growth,  enabling  a  lower  rate  of 
water  to  supply  the  requirements  of  the  plant ;  or  to  greater  root 
attraction  for  water  by  some  plants,  causing  a  larger  flow  of  water 
into  the  one  plant  than  in  the  other,  under  the  same  conditions  of 
soil  moisture;  or  to  differences  in  the  amount  of  water  transpired. 

During  a  severe  drouth,  the  California  Experiment  Station2 
determined  the  amount  of  water  in  a  large  number  of  soils,  where 
plants  were  doing  well,  or  were  suffering.  California  soils,  it 
must  be  recalled,  are  different  from  soils  of  humid  climates,  there 

1  Proc.  Am.  Soc.  Agr.,    1910,  p.   138;    1911,    p.  250;    Bui.  230,  Bureau 
of  Plant  Industry. 

-  Report  1897,  p.  95. 
10 


138  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

being  no  distinction  between  subsoil  and  surface  soil,  the  roots 
thus  being  able  to  strike  deep  into  the  soil.  For  this  reason 
smaller  quantities  of  water  may  suffice  for  crops.  The  results  are 
as  follows : 


Available  water  per  cent. 

Doing  well 

Suffering 

Apricots 
Citrus 
Almonds 
Pears 
Wheat 
Sugar  Beets 

Citrus 
Almonds 
Barley 
Wheat 

I-  1   ^ 

1   '  -0     • 
T    ^-2 

*«O  *     ' 

3  .A      

q. 
4_c     

<;-6  . 

Root  Area  of  Plants. — The  greater  the  volume  of  soil  occupied 
by  the  roots,  the  greater  the  quantity  of  water  (and  also  of  plant 
food)  at  the  disposal  of  the  plant.  Hence  operations  which 
deepen  the  surface  soil  or  loosen  the  subsoil,  so  as  to  allow  the 
roots  to  penetrate  more  deeply,  have  a  favorable  effect  upon  the 
amount  of  water  offered  to  the  plant.  The  volume  of  soil 
occupied  by  plants  depends  upon  the  nature  of  the  plant. 

Water-Table. — The  water-table  is  the  depth  at  which  the  soil  is 
saturated  with  water,  and  is  indicated  by  the  depth  of  the  water 
surface  in  shallow  wells,  which  is  slightly  below  the  water-table. 
The  water  in  the  water-table  is  termed  ground  water.  All  perman- 
ent lakes  and  ponds  may  be  considered  as  extension  of  the  water- 
table  above  the  surface  of  the  land.  The  surface  of  the  water- 
table  follows,  in  a  general  way,  the  contour  of  the  land,  standing 
highest  where  the  ground  is  highest,  and  low  where  the  land  is 
low.  Land  at  the  foot  of  hilly  ground  may  receive  a  continuous 
supply  of  underground  water,  even  in  time  of  drought. 

If  a  bed  of  impervious  clay  is  present  in  the  subsoil,  the  under- 
ground water  accumulates  on  its  surface.  The  water  level  may 
generally  be  lowered  by  drainage  ditches  or  tile  drains. 

The  height  of  the  water-table  depends  upon  the  character  of 
the  soil,  the  rainfall,  and  the  climate.  It  usually  fluctuates, 
rising  during  wet  seasons  and  sinking  during  a  drought.  \Yhen 
the  height  of  the  saturated  layer  reaches  a  certain  point,  discharge 
takes  place  in  the  form  of  springs  or  as  general  drainage. 


THE  SOIL  AND  WATER  139 

If  the  water-table  is  only  a  few  inches  beneath  the  surface,  we 
have  a  swamp  or  bog;  at  one  and  a  half  to  three  feet  in  depth, 
we  ha\e  a  wet  soil  in  which  some  plants,  especially  grasses,  may 
flourish.  A  depth  of  four  to  eight  feet  is  favorable  to  agricultural 
conditions,  though  in  many  regions  the  water-table  is  much  lower 
than  this. 

In  general,  agricultural  plants  are  injured  if  their  roots  are  im- 
mersed for  any  length  of  time  in  the  ground  water,  though  many 
plants  may  send  down  roots  to  this  water. 

Gains  of  Water  by  the  Soil. — The  chief  ways  in  which  the  soil 
may  gain  water  are  by  rainfall  and  irrigation.  In  addition,  ground 
water  may  be  brought  up  to  within  reach  of  the  plant  roots 
by  capillary  action. 

Regions  having  more  than  20  inches  rainfall  are  said  to  have 
a  humid  climate.  The  character  of  the  rainfall  must  be  con- 
sidered as  well  as  the  total  quantity.  If  it  is  heavy 
and  infrequent,  a  large  proportion  of  the  water  will 
run  off  on  the  surface  and  the  region  may  possess  more 
characteristics  of  an  arid  climate  than  a  region  with  a  moderate 
rainfall  well  distributed. 

The  amount  of  water  gained  from  rain  depends  upon  the 
nature  and  the  extent  of  the  rainfall,  the  drainage,  etc.  A  heavy, 
rapid  rainfall  may  saturate  the  surface  and  flow  off  without  any 
large  quantity  sinking  into  the  soil.  A  slight  rain  may  decrease 
the  water  content  of  the  soil  by  establishing  such  capillary  connec- 
tion between  surface  soil  and  lower  layers,  as  to  bring  water  to 
the  surface  which  is  lost  by  evaporation. 

If  the  surface  of  the  soil  is  compact,  the  rain  may  flow  off 
instead  of  penetrating  the  soil;  but  if  the  soil  is  loose,  it  will 
absorb  considerable  quantities  of  rain. '  One  method  of  prevent- 
ing the  washing  of  hilly  land  consists  in  deep  plowing  or  subsoil 
plowing,  so  that  the  water  will  sink  into  the  soil  instead  of  run- 
ning off.  In  regions  of  slight  rainfall,  where  it  is  desirable  to 
save  all  the  rain,  the  subsoil  is  stirred,  and  packed ;  this  increases 
the  capillarity  of  the  soil  and  its  power  of  holding  water.  These 
are  the  methods  of  dry  farming.1 
1  See  Dry  Farming,  by  Widstoe. 


140  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Capillary  Action. — If  the  water-table  of  the  soil  is  so  low  that 
capillary  action  cannot  raise  water  to  the  plant  roots,  it  has  no 
effect  upon  the  plant.  If  it  is  within  such  distance  that  water 
can  be  raised  to  the  soil's  surface,  the  water  raised  by  capillarity 
will  tend  to  replace  the  water  lost  by  evaporation  and  transpira- 
tion. The  extent  to  which  this  replacement  takes  place  depends 
upon  the  relative  rates  of  evaporation  and  transpiration,  and  the 
rate  of  capillary  action. 

King1  studied  the  amount  of  water  which  can  be  brought  up- 
ward by  capillary  action,  using  cylinders  4  feet  high  and  one  foot 
in  diameter,  which  could  be  supplied  with  water  from  below.  The 
cylinder  was  partly  filled  with  water,  soil  dropped  in  and  stirred, 
and  the  operation  repeated  until  the  cylinder  was  filled.  The  water 
level  was  then  lowered  to  one  foot  below  the  surface,  and  main- 
tained at  this  point,  while  the  surface  of  the  cylinder  was  exposed 
for  eight  days  to  a  strong  current  of  air,  and  the  quantity  of  water 
evaporated  determined.  The  evaporation  was  determined  for 
depths  of  i,  2,  3,  and  4  feet  of  the  water-table.  At  the  depth  of 
4  feet,  the  average  evaporation  from  a  fine  sand  and  a  clay  loam 
was  0.9  pounds  per  day  and  square  foot.  In  order  for  this 
experiment  to  be  complete,  it  would  be  necessary  to  prove  that 
this  quantity  of  water  passed  upward  from  the  water-table.  The 
evaporation  of  the  water  may  have  been  due,  in  part,  to  the 
natural  drying  of  the  soil,  although  it  decreased  as  the  water-table 
was  lowered.  In  Wisconsin,  crops  in  this  soil  suffer  considerably 
from  drought,  though  the  water-table  is  only  five  feet  from  the 
surface,  showing  that  in  the  natural  condition  the  soil  is  able  to 
raise  but  little  water  even  a  distance  of  five  feet. 

The  effect  of  capillary  action  in  bringing  up  water  is  also  shown 
by  the  Rothamsted  drain  gauges.  The  shallow  one  is  20  inches 
deep,  the  deeper  one  40  inches.  On  an  average  of  twenty-five 
years,  the  annual  evaporation  from  the  deeper  gauge  is  only  0.6 
inches  greater  than  from  the  shallow ;  this  probably  represents  the 
quantity  of  water  brought  to  the  surface  from  below  the  depth  of 
20  inches. 

1  Report  Wisconsin  Station  1889-1890. 


34. — Corn  on  heavy  clay  soil  (a]  undrained  (b)  tiles  70  feet 
apart  (c)  tiles  44  feet  apart.     Wisconsin  Station. 


142  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  roots  of  plants,  however,  may  sometimes  extend  to  con- 
siderable depths,  and  the  presence  of  the  water-table  at  a  mod- 
erate distance  from  the  surface,  is  thus  an  advantage. 

If  moist  air  comes  in  contact  with  a  cold  surface  it  will  deposit 
water.  A  soil  may  gain  water  from  the  air  when  the  air  is  moist 
enough  and  the  surface  of  the  soil  cool  enough.  It  has  been 
thought  that  water  is  sometimes  distilled,  as  it  were,  from  the 
lower  layers  of  the  soil  into  the  upper. 

The  monthly  drainage  from  Mr.  Greaves  drain  gauge1  in  Eng- 
land, filled  with  gravel  and  free  of  vegetation,  has  in  fourteen 
years  exceeded  the  monthly  rainfall  nineteen  times;  twice  in 
December,  seven  times  in  January,  seven  times  in  February,  and 
three  times  in  March.  The  amount  of  water  condensed  from  the 
air  must,  therefore,  have  been  in  each  case  more  than  that  lost  by 
evaporation  from  the  soil,  and  may  therefore  increase  the 
moisture  of  the  soil.  In  Texas  very  heavy  dews  have  been 
observed  at  various  times.  Drain  gauges  in  England  sometimes 
run  more  water  than  falls  as  rain,  especially  in  January, 
February,  and  March. 

Losses  of  Water  from  the  Soil. — The  water  which  comes  to  the 
soil  is  lost  in  several  ways.  Part  flows  away  without  penetrating 
the  soil,  as  surface  water.  Part  percolates  through  the  soil  to 
the  water-table  and  reappears  in  drains,  wells  or  springs,  or 
passes  through  subterranean  channels  to  the  sea;  this  may  be 
called  percolation  water.  Another  portion  of  the  water  is  evapo- 
rated from  the  soil  into  the  atmosphere.  Finally,  the  water  taken 
up  by  plants  is  passed  off  through  their  leaves  into  the  air 
(transpiration). 

The  proportion  of  the  rainfall  which  passes  off  as  surface  water 
depends  upon  (a)  the  character  and  condition  of  the  soil;  (b) 
the  slope  of  the  land;  (c)  the  amount  and  duration  of  the  rain- 
fall. If  the  soil  is  loose  and  porous,  either  naturally,  or  rendered 
so  by  cultivation,  a  larger  amount  of  water  will  penetrate  it.  The 
slope  of  the  land  determines  the  rate  at  which  the  water  runs  off ; 
the  shorter  the  time  of  contact  between  soil  and  water,  other 
1  Warington,  Physical  Properties  of  the  Soil. 


THE  SOIL  AND  WATER 


things  being  equal,  the  smaller  will  be  the  amount  of  water 
absorbed  by  the  soil.  The  greater  the  quantity  of  water  pre- 
cipitated in  a  given  period  of  time,  the  larger  the  proportion  of  it 
will  run  off  as  surface  water.  The  more  rapidly  the  water  runs 
off,  the  more  soil  it  carries  along  with  it,  and  the  more  likely  it  is 
to  do  damage  by  washing. 

Percolation. — The  rate  at  which  water  passes  through  the  soil 
depends  upon  the  character  of  the  soil  and  the  treatment  to  which 
it  has  been  subjected.  Sands  allow  water  to  percolate  rapidly, 


3  Drain  Gauges — 

•  Each  7  feet  3- 12  in.  x  6  feet  =  ^th  acre  area : 
Respectively  20,  40,  and  60  inches  depth  of  soil, 
collectors,  each  holding  Drainage       =     0*500  in. 
Gauge-tubes  graduated  to    ..          ..     0-002  in. 
Overflow  tank  to  hold  Drainaee.         .=.    2- 000  ins. 

Fig-  35- — Drain  gauges,  Rothamsted,  England. 

and  since  they  usually  have  a  low  capillary  power,  they  often 
suffer  from  drought.  Some  clays  allow  water  to  pass  through 
so  slowly  that  they  remain  wet  and  heavy,  do  not  warm  up 
quickly,  and  are  often  hard  to  work.  The  amount  of  water 
which  percolates  may  be  decreased  by  increasing  the  water  cap- 
acity of  the  soil  or  subsoil. 

Drain  Gauges. — Drain  gauges  are  used  to  study  the  gains  and 


144 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


I 

vl 

L 


O    •; 
3"7//e:  •'•'•  •(  •'•:•'••(<'. 


Bnass* 

ftpe    Q 


. 

• 

**3" 

^Graote 

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| 

J 

L 

,'-':• 

AV 

Q 

v> 

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C/nofer 


Fig.  36.  —Concrete  tubs  for  soil  investigations,  Neu  York 
(Cornell)  Station. 


THE:  SOIL  AND  WATER  145 

losses  of  water  by  percolation  and  evaporation.  The  composition 
of  the  drainage  water  may  also  be  studied. 

A  drain  gauge  is  a  water-tight  vessel  rilled  with  soil  and  ex- 
posed to  the  rain  under  natural  conditions.  The  water  which 
passes  through  a  given  depth  of  soil  is  collected,  measured,  and 
otherwise  examined,  as  desired.  The  soil  may  be  kept  bare,  or 
cultivated  or  planted  to  various  crops.  The  drain  gauges  at 
Rothamsted  are  filled  with  undisturbed  soil  of  that  place.  Excava- 
tions were  made  along  the  side  of  the  block  of  earth  desired;  it 
was  bricked  up  and  isolated.  Each  drain  gauge  consists  of  a 
rectangular  mass  of  heavy  loams  with  flints,  of  an  area  of  i/iooo 
acre,  20,  40,  and  60  inches  deep,  respectively.  All  the  rainfall 
either  passes  through  this  mass  of  earth  or  evaporates.  Drain 
gauges  filled  with  loose  earth  represent  unnatural  conditions,  and 
time  should  be  allowed  for  the  earth  to  consolidate  before 
measurements  are  begun. 

Another  method  of  studying  drainage  waters  is  to  measure  the 
water  going  off  through  tile  drains,  but  this  is  not  a  good  method, 
since  only  the  excess  of  ground  water  passes  off  through  the 
drain.  A  large  portion  of  the  percolating  water  passes  into  the 
country  drainage. 

Evaporation. — The  rate  at  which  water  is  lost  by  evaporation 
depends  upon  the  nature  and  moistness  of  the  soil,  its  capillary 
condition,  the  temperature,  velocity  of  wind,  humidity  of  air,  etc. 

The  wetter  the  soil,  the  less  the  humidity  of  the  air,  the  greater 
the  velocity  of  the  wind,  and  the  higher  the  temperature,  the 
greater  is  the  loss  by  evaporation. 

If  the  upper  layer  of  the  soil  is  loose  and  porous,  it  will  dry  out 
quickly,  and  the  rate  of  loss  will  then  be  influenced  by  the  rate  at 
which  water  is  brought  to  the  surface  by  capillary  action. 
Evaporation  is  greatly  checked  if  the  connection  between  the  top 
soil  and  the  under  layer  is  broken  by  cultivation.  Evaporation  is. 
also  influenced  by  the  rapidity  with  which  the  water  penetrates 
the  soil.  Much  larger  quantities  of  water  will  be  lost  by 
evaporation  if  the  water  is  retained  near  the  surface,  than  if  it 
sinks  into  the  soil. 


146 


PRINCIPLES  OF  AGRICULTURAL,  CHEMISTRY 


The  annual  evaporation  from  the  bare  soil  in  the  Rothamsted 
rain-gauges  is  apparently  unaffected  by  the  amount  of  rainfall. 
During  nine  years  the  rainfall  varied  from  22.9  to  42.7  inches ; 
the  evaporation  from  the  shallow  gauge  varied  from  16.6  to  18.4 
inches,  while  the  percolation  varied  from  5.6  to  25.5.  inches. 

The  losses  of  water  from  soil  carrying  vegetation  is  greater 
than  from  a  bare  soil.  In  the  rotation  of  crops,  it  is  necessary 
to  consider  this  fact.  For  example,  King1  determined  the  per- 
centage of  water  in  two  portions  of  a  field  about  to  be  planted  to 
corn ;  one  portion  had  previously  been  a  bare  fallow,  the  other 
had  carried  clover.  The  clover  land  contained  much  less  water 
than  the  bare  fallow  land,  and  the  corn  on  the  bare  fallow  would 
thus  be  far  better  able  to  stand  a  summer  drought.  One  injurious 
effect  of  weeds  is  to  remove  water  from  the  soil. 

Relation  of  Water  Content  to  Evaporation. — In  the  following 
table  (by  Schubler)  the  amount  of  water  absorbed  by  soils  is  com- 
pared with  the  amount  of  evaporation  during  four  hours : 


Percentage 
of  water  held 
by  soil 

Percentage  of 
water  present 
evaporated 

25 
27 
29 

51 
6r 
70 

85 
89 
181 
256 

88.4 
71-7 
75-9 
45-7 
34-9 
31-9 
28.0 

24-3 
25-5 
10.8 

L/ime  sand  

L/oam   

Fine  carbonate  of  linie  

It  is  evident  that  the  finer  soils  have  not  only  a  greater  water 
capacity,  but  also  allow  less  evaporation  to  take  place. 

Control  of  Water. — The  control  of  water,  so  that  plants  may 
at  all  times  receive  the  optimum  amount,  or  as  near  it  as  possible, 
is  one  of  the  most  important  parts  of  agricultural  practice  and 
the  chief  object  of  many  operations  of  tillage. 

Control  of  the  water  supply  is  exercised  by  storing  water  in  the 
1  The  Soil,  I9r. 


THE:  SOIL  AND  WATER  147 

soil,  by  irrigation,  by  improving  capillary  conditions,  by  preven- 
tion of  loss,  by  decreasing  transpiration,  by  drainage.  In  regions 
where  rainfall  is  deficient,  especially  during  the  crop  season,  it 
may  be  necessary  to  store  up  the  rain  as  much  as  possible.  Sur- 
face water  may  be  conserved  by  plowing  the  soil  before  the  rainy 
season.  Due  regard  should  be  paid  to  proper  ditching,  to  prevent 
washing.  The  subsoil  may  also  be  plowed  and  in  arid  regions  (dry 
land  farming)  it  is  packed  after  plowing  so  as  to  restore  its  capill- 
ary spaces.  In  some  dry  regions  a  crop  is  grown  only  every  alter- 
nating year.  The  first  year,  the  soil. is  plowed,  and  the  surface  is 
kept  loose  and  porous  so  as  to  reduce  the  loss  by  evaporation; 
the  second  year  the  crop  is  grown. 

The  capillary  condition  of  soils  which  are  too  loose  and  porous, 
and  also  those  too  heavy  and  compact,  is  improved  by  incorporat- 
ing vegetable  matter  with  the  soil.  Capillary  conditions  may  also 
be  improved  by  plowing  of  soil  or  subsoil  when  in  suitable  condi- 
tion. 

Under-drainage,  by  aerating  the  soils,  allows  roots  to  go  deeper, 
and  so  places  at  their  disposal  a  larger  volume  of  soil  containing 
plant  food  and  water.  Since  an  excess  of  water  keeps  the  soil 
cold,  drainage  causes  the  land  to  warm  up  sooner  in  the  spring. 

Losses  of  water  by  evaporation  may  be  prevented  by  tillage. 
Surface  cultivation  of  the  soil  breaks  up  the  capillary  pores,  and 
prevents  water  rising  to  the  surface.  The  following  table  of 
King  illustrates  the  effect : 

Water  evaporated 

in  221  days. 

Inches 

Compact  soil 7.98 

Stirred  i  inch 5.09 

Stirred  2  inches 4.20 

Stirred  3  inches 3.66 

Stirred  4  inches 3.60 

Compacting  the  soil  by  rolling  increases  evaporation,  since  it 
increases  the  efficiency  of  the  capillary  pores.  Rolling  after  plant- 
ing grass  seed  is  often  advantageous,  as  it  brings  moisture  to  the 
surface  to  sprout  the  seed. 

The  destruction  of  weeds  prevents  loss  by  evaporation.     In 


148  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

orchards  it  is  often  advisable  to  keep  the  soil  cultivated  and  free 
from  weeds  or  crops  in  order  to  prevent  injury  to  the  trees  from 
want  of  water. 

Wet  and  Dry  Soils. — Dry  soils  are  composed  of  coarse  par- 
ticles, with  free  percolation  and  little  power  of  retaining  water. 
Wet  soils  are  composed  of  very  fine  particles  having  an  enormous 
extent  of  intersurface  and  offering  great  resistance  to  the  passage 
of  water. 

The  character  of  the  subsoil  is  also  of  great  influence.  A  sandy 
surface  soil  acts  differently  when  it  has  a  subsoil  of  loam  or  clay. 
A  clay  soil  is  no  longer  wet  when  it  has  an  open  porous  subsoil. 
Whether  the  soil  is  level  or  on  a  hill  side  or  receives  the  drainage 
of  higher  land,  influences  the  water  held  in  the  soil. 

The  most  suitable  physical  composition  of  a  soil  depends  on  the 
climate  and  the  situation  in  which  it  is  placed ;  soils  of  great  value 
in  one  situation  may  be  of  little  value  in  another.  A  clay  land 
which  can  be  used  only  for  pasture  with  an  available  rainfall  of 
forty  inches,  may  be  used  to  great  advantage  where  the  rainfall  is 
only  twenty-five. 

Effect  of  Cultivation  and  Manure. — Shallow  surface  cultiva- 
tion conserves  moisture.  Rolling  compacts  the  soil  and  causes 
water  to  rise  to  the  surface.  Fall  plowing  allows  water  to 
penetrate  the  soil,  and  if  followed  by  surface  cultivation,  may 
allow  a  balance  of  water  to  be  carried  over  to  the  next  season. 
Spring  plowing,  if  followed  by  dry  weather, causes  loss  o"f  moisture 
by  evaporation ;  it  should  therefore  be  followed  by  surface  cultiva- 
tion. Manure  or  straw,  spread  as  a  mulch,  prevents  loss  of  water 
by  evaporation. 


CHAPTER  VIII. 


CHEMICAL  CONSTITUENTS  OF  THE  SOU. 

The  soil  is  composed  of  disintegrated  rocks,  containing  organic 
matter.  Its  constituents  are,  therefore,  inorganic  and  organic. 

The  inorganic  constituents  consist  of  the  original  rock  minerals, 
products  of  their  partial  decomposition,  and  their  final  products 
of  decomposition.  The  organic  constituents  consist  of  unchanged 
residues  of  plants  and  animals,  intermediate  substances  formed  by 
the  action  of  bacteria,  molds,  and  other  agencies,  and  the  final 
products  of  decomposition,  namely,  carbon  dioxide  and  water. 

Primary  and  Secondary  Minerals. — By  far  the  greater  portion 
of  the  crust  of  the  earth,  and  of  the  soils  thereon,  is  composed 
of  silica,  and  combinations  of  silica  with  bases,  termed  silicates. 
A  large  number  of  silicates  are  known,  many  of  which  are  very 
complex  in  constitution.  Igneous  rocks,  which  are  the  oldest 
rocks,  are  composed  entirely  of  silica  or  silicates.  Primary  sili- 
cates undergo  chemical  changes,  under  the  action  of  the  air, 
water,  and  other  natural  agencies,  whereby  other  silicates  and 
other  minerals  are  formed.  The  unchanged  minerals  found  in 
igneous  rocks  are  for  this  reason  termed  primary  minerals,  and 
those  produced  from  them  by  chemical  agencies  are  called 
secondary  minerals. 

Soils  are  composed  of  three  classes  of  minerals : 
(a-)   Primary   minerals,    the   unchanged   minerals    of   igneous 
rocks,  not  easily  affected  by  chemical  reagents. . 

(b)  Hydrated  silicates,  which  are  intermediate  products  of  the 
decomposition  of  the  primary  minerals,  and  more  easily  acted  on 
by  chemical  reagents  and  the  roots  of  plants. 

(c)  Final  products  of  weathering. 

The  relative  abundance  of  these  three  classes  of  minerals  in  the 
soil  will  depend  on  the  age  and  nature  of  the  rock  material  and 
the  nature  and  activity  of  the  weathering  agencies.  Old  soils  are 
naturally  more  highly  decomposed  than  are  soils  of  more  recent 
origin.  Transported  soils  consist  of  a  greater  variety  of  minerals 


I5O  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

than  soils  formed  from  rocks  in  place,  and  not  mixed  with  the 
products  of  the  decomposition  of  other  rocks. 

Primary  Minerals.— Dr.  F.  W.  Clarke,1  Chemist  to  the  U.  S. 
Geological  Survey,  has  calculated  the  relative  abundance  of  the 
minerals  of  igneous  rocks  to  be  as  follows : 

Per  cent. 

Feldspars   59  5 

Hornblende  and  pyroxenes 16.8 

Quartz 1 2.0 

Biotite    3.8 

Titanium  minerals 1.5 

Apatite o.  6 

Less  frequent  minerals 5.8 

Quartz  is  crystallized  silicon  dioxide  (SiCX)  and  is  widely  dis- 
tributed in  nature.  It  is  insoluble  in  water  or  any  acid  except 
hydrofluoric.  It  is  very  hard  and  not  easily  broken.  It  cannot 
be  dissolved  or  decomposed  by  natural  agencies,  although  it  may 
be  reduced  to  a  fine  powder.  It  is  often  found  as  pebbles,  sand, 
and  sometimes  a  very  fine  powder,'  in  residues  from  rocks  which 
have  otherwise  undergone  serious  changes.  It  is  of  common 
occurrence  in  soils.  It  has  no  value  to  plants  as  food. 

Felspars  are  double  silicates  of  alumina  with  potash,  soda,  or 
lime.  They  are  widely  distributed,  making  up  about  sixty  per 
cent,  of  the  average  igneous  rock.  The  chief  varieties  of  felspar 
are: 

Orthoclase,  a  potash  felspar KAlSi3O8 

Albite,  a  soda  felspar NaAlSi3O8 

Anorthite,  a  lime  felspar CaAl2Si.jO8 

A  number  of  intermediate  varieties  occur,  such  as  oligoclase,  a 
soda-lime  felspar. 

Felspars  are  not  acted  upon  by  strong  acids  (except  hydro- 
fluoric) and  can  only  be  brought  into  solution  after  fusion  with 
carbonate  of  soda,  or  by  decomposition  with  hydrofluoric  acid. 
They  are  slowly  decomposed  by  weathering  agencies.  If  finely 
ground  felspar  is  brought  in  contact  with  water  containing 
phenolphthalein,  the  liquid  assumes  a  red  color.  This  is  due  to 
the  solution  of  a  small  amount  of  soda  and  potash,  which,  being 
1  Bulletin  419,  p.  9. 


CHEMICAL  CONSTITUENTS  OF  THE  SOU,  151 

alkaline,  turn  the  phenolphthalein  red.  A  number  of  other 
minerals  behave  in  the  same  way.  The  quantity  of  alkali  which 
goes  into  solution  is,  however,  very  small.  Only  a  small  fraction 
of  felspar  is  dissolved  by  the  concentrated  hydrochloric  acid  used 
in  soil  analysis  and  about  i  to  4  per  cent,  of  the  total  potash.  The 
potash  held  in  felspar  has  only  :i  slight  value  to  plants,  as  it  is  dis- 
solved very  slowly. 

Micas  are  primary  silicates,  which  are  easily  split  into  thin, 
flexible,  and  elastic  leaves.  They  have  a  complex  and  varying 
composition,  being  silicates  of  alumina  with  potash,  lithia, 
magnesia,  iron  or  manganese.  Muscovite  is  light  colored  potash 
mica,  K2Al6Si6  Ol222H2O.  Biotite,  a  dark  colored  mica,  is  a  com- 
plex hydrated  silicate  of  alumina,  iron,  potash,  and  magnesia. 

Micas  are  decomposed  very  slowly.  They  persist  for  a  long 
time  after  the  other  rock  minerals  have  been  entirely  changed  by 
weathering.  Almost  any  soil  derived  from  granite  contains  flakes 
of  mica,  which  are  more  easily  seen  if  oxides  of  iron  are  removed 
with  a  little  hydrochloric  acid.  Micas  aid  in  the  decomposition 
of  rocks  in  which  they  are  present,  by  allowing  water  to  percolate 
into  their  fissures.  Mica  is,  to  a  large  extent,  dissolved  by  strong 
acids,  and  it  is  probable  that  the  plant  food  it  contains  is  more 
easily  used  than  that  of  felspar. 

Hornblendes  and  Pyroxenes  include  a  number  of  silicates  of 
varying  composition,  though  with  related  properties.  They  are 
complex  silicates  of  magnesia,  alumina,  lime,  and  iron.  They  are 
usually  green,  brown,  or  black  in  color.  They  are  easily  affected 
by  natural  agencies.  Olivine  is  a  silicate  of  iron  and  magnesia 
(MgFe)2Si2O4. 

Apatite  Ca3PO4Ca(ClF)2  is  a  crystallized  phosphate  of 
lime.  It  is  considered  to  be  the  chief  form  in  which  phosphoric 
acid  occurs  in  igneous  rocks. 

Secondary  Minerals. — The  minerals  formed  from  the  primary 
minerals  by  processes  of  combination  with  water,  by  solution, 
oxidation,  or  by  partial  or  complete  decomposition,  are  termed 
secondary  minerals.  They  occur  in  rocks  formed  by  decomposi- 
tion of  the  igneous  rocks,  and  in  soils.  A  few  of  them  are 
described  in  the  following  paragraphs. 


152 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Hydrated  Silicas  are  formed  by  the  deposition  of  silica  from 
aqueous  solutions.  From  many  silicates  water  dissolves  silica, 
which  may  be  deposited  as  various  forms  of  hydrated  silica. 
Hydrated  silicas  are  probably  present  in  some  soils. 

Hydrated  Silicates  are  produced  by  combination  of  water  with 
primary  or  secondary  silicates,  with  or  without  loss  of  matter  by 
solution.  The  complex  hydrated  silicates  are  more  easily  decom- 
posed, and  otherwise  enter  into  reactions  much  more  readily  than 
the  primary  silicates,  from  which  they  were  formed.  They  are 
also  more  easily  decomposed  by  acids.  Hydrated  silicates  appear 
to  be  of  considerable  importance  in  the  soil.  A  great  number  of 
hydrated  silicates  are  known. 

Zeolites  are  hydrated  silicates  of  alumina,  with  varying  amounts 
of  potash,  soda,  lime,  etc.,  produced  by  hydration  and  decomposi- 
tion of  many  varieties  of  minerals.  They  are  easily  decomposed 
by  acids.  A  large  number  of  zeolites  are  known.  They  take 
part  in  some  important  reactions  which  occur  in  the  soil,  especially 
the  fixation  of  potash. 

Chabazite  (HK)2CaAl2Si5O15+6H2O,  stilbite  (CaNa)2Al2Si6- 
Q16+6H2O,  analcite  Na2Al2Si4O12+2H2O  and  prehnite  HeCa2- 
Al4Si3O12,  are  hydrated  silicates  belonging  to  the  zeolite  class. 
They  are  soluble  in  hydrochloric  acid,  the  silica  being  separated. 
When  brought  in  contact  with  salts  of  potash,  they  remove  some 
of  the  potash  from  solution  and  replace  it  with  equivalent 
quantities  of  lime  or  soda.  For  example,  the  minerals  named 
below1  were  treated  with  a  strong  solution  of  sulphate  of  potash, 
washed  and  subjected  to  analysis : 


Original  mineral 

After  treatment 

Per  cent,  potash 

0.25 
0.17 

o.47 
0.90 

I.OO 

Per  cent,  potash 

3-95 
4.09 

1-54 
4.82 

5.96 

Stilbite  anotVier  sample  

Cliaba/ite 

1  Texas  Station,  Bulletin  106,  p.  u. 


CHEMICAL   CONSTITUENTS  OF   THE  SOU,  153 

The  reaction  may  be  represented  as  follows : 

Chabazite  +  K2SO4  =  K  Chabazite  +  CaSO4. 

The  reaction  is  reversible.  When  treated  with  sulphate  of 
lime,  or  other  lime  salts,  the  absorbed  potash  is  partly  replaced  by 
lime. 

K  Chabazite  +  CaSO4  —  K,SO4  +  chabazite. 

The  extent  of  the  change  depends  on  the  conditions  of  the 
experiment  and  will  be  discussed  under  the  topic  of  fixation  by 
the  soil.  It  is  possible  that  other  hydrated  silicates  besides  zeolites 
take  part  in  the  fixation  of  potash. 

Finite  is  a  hydrated  silicate  of  alumina  and  potash,  resulting 
from  the  decomposition  of  felspar  and  some  other  minerals. 

Kaolinite  is  a  hydrated  silicate  of  alumina  having  the  formula 
AlaSi2O72H2O.  Kaolin  is  largely  composed  of  kaolinite.  Clay 
contains  kaolinite.  Kaolin  may  be  considered  as  a  final  product 
of  weathering  of  felspar  and  other  silicates  containing  alumina. 
The  reaction  which  occurs  in  the  formation  of  kaolin  by  the  action 
of  water  containing  carbon  dioxide  upon  felspar,  may  be  written 
as  follows : 
K2Al2Si6O16  +  H2O  +  CO2  ==  Al_Si2O-  +  K2CO3  +  H2Si4O9. 

If  lime  or  soda  is  present,  its  carbonate  is  formed  in  this  decom- 
position. The  lime  or  soda  may  be  converted  into  sulphate  or 
chloride  if  sulphur  or  chlorine  is  present  in  the  rock. 

Chlorites  are  hydrated  silicates  of  alumina,  magnesia,  or 
iron.  They  are  products  of  the  decomposition  of  hornblende, 
augite,  and  magnesium  micas.  Further  decomposition  results  in 
serpentine. 

Talc  and  Serpentine  are  hydrated  silicates  of  magnesia.  They 
are  soft,  with  a  greasy  feeling.  Serpentine  results  from  the  decay 
of  olivine,  and,  though  less  often,  from  augite  or  hornblende. 

Glauconite  is  a  hydrated  silicate  of  alumina  and  iron,  contain- 
ing a  small  quantity  of  lime,  magnesia,  potash,  soda,  and  phos- 
phoric acid.  It  often  occurs  as  grains  of  a  green  color,  and  is 
termed  green  sand.  Green  sand  marl  is  a  mixture  of  glauconite 
and  calcium  carbonate. 

Carbonates  of  Lime  and  Magnesia  result  from  the  action  of 
1 1 


154  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

carbon  dioxide  and  water  upon  many  silicates  containing  lime 
and  magnesia.  Both  compounds  are  slightly  soluble  in  water, 
and  more  soluble  in  water  containing  carbon  dioxide.  All  waters 
which  have  been  in  contact  with  the  earth  contain  lime  and 
magnesia.  Large  limestone  deposits  have  been  formed  by  shell 
fish  and  other  organisms,  which  withdraw  carbonate  of  lime  from 
solution.  Many  of  our  most  fertile  soils  are  derived  from  lime- 
stone deposits,  or  contain  two  per  cent,  or  more  of  carbonate  of 
lime.  Carbonate  of  lime  is  an  important  soil  constituent.  Its 
presence  flocculates  clay  and  makes  clay  soils  less  sticky  and  more 
easily  worked.  In  calcareous  soils,  the  phosphoric  acid  and 
potash  is  generally  held  in  more  available  forms.  Carbonate  of 
lime  unites  more  or  less  slowly  with  soluble  phosphates  which 
may  be  present  or  introduced  into  the  soil,  forming  compounds 
which,  while  less  soluble  than  before  and  of  less  value  to  plants, 
are  more  soluble  and  apparently  of  greater  value  to  plants  than 
the  soil  compounds  of  phosphoric  acid  with  iron  or  aluminium. 
Other  actions  of  lime  will  be  referred  to  later. 

Sulphate  of  lime  is  found  in  small  quantities  in  many  soils,  in 
large  quantities  in  a  few  soils. 

Iron  Minerals. — By  the  decomposition  of  silicates  containing 
iron,  various  compounds  of  iron  are  produced,  mostly  oxides  and 
carbonates.  These  bodies  ordinarily  occur  in  the  soil,  often 
giving  the  soil  a  red,  brown,  or  yellow  color,  depending  on  the 
stage  of  oxidation.  Hematite  is  anhydrous  ferric  oxide  Fe^CX, 
red  when  finely  powdered.  Magnetite  Fe;,O4  is  black  oxide  of 
iron.  Limonite  is  hydrated  ferric  oxide  2Fe2O,3H2O,  and  has  a 
yellow  or  brown  color.  Siderite  is  carbonate  of  iron,  and  is  gray 
or  brown  in  color.  It  is  affected  with  difficulty  by  cold  acids, 
easily  by  hot  acids.  The  bulk  of  the  phosphoric  acid  of  ordinary 
soils  is  probably  in  combination  as  basic  phosphates  of  iron  or 
aluminium,  or  in  basic  silicates  of  these  elements.  Such  forms  of 
combination  are  apparently  not  as  valuable  to  the  plant  as  the 
calcium  phosphates.  Limonite  is  deposited  from  water  contain- 
ing iron.  Oxides  of  iron  are  reduced  by  decaying  vegetable 
matter  and  combine  with  carbonic  acid  to  form  ferrous  car- 


CHEMICAL  CONSTITUENTS  OF  THE  SOIL  155 

bonate,  which  dissolves  in  water.  On  exposure  to  the  air,  the 
ferrous  carbonate  is  oxidized  and  is  precipitated  as  insoluble 
hydrated  ferric  oxide.  This  action  does  not  take  place  in  soils 
containing  carbonate  of  lime.  A  layer  of  hard  pan,  consisting  of 
rock  grains  cemented  by  limonite,  is  often  formed  below  poorly 
drained  soils. 

Pyrite  FeS2  has  a  light  yellow  color  and  is  often  called  fool's 
gold.  It  is  easily  oxidized  to  sulphates  by  atmospheric  agencies. 
It  is  sometimes  formed  in  badly  aerated  soils. 

Phosphate  Minerals. — Phosphates  do  not,  as  a  rule,  occur  in 
large  quantities  in  the  soil,  but  are  important  on  account  of  their 
indispensability  to  plant  life.  The  important  phosphate  minerals 
are:  Apatite,  or  crystallized  calcium  phosphate  Ca3(PO4)2;  phos- 
phate rock,  or  amorphous  calcium  phosphate ;  vivianite,  which  is 
hydrated  phosphate  of  iron;  wavellite,  or  hydrated  phosphate  of 
alumina.  The  three  phosphates  named  last  probably  occur  in 
soils.  A  large  number  of  mineral  phosphates  are  known.  Dr. 
F.  W.  Clarke,  of  the  U.  S.  Geological  Survey,  assumes  that  all 
the  phosphoric  acid  of  igneous  rocks  is  present  as  apatite.  As 
stated  above,  phosphates  are  also  found  in  the  soil  as  basic  com- 
pounds of  iron  and  aluminium.  Organic  phosphorus  compounds 
are  also  present  in  the  soil. 

Soluble  Salts. — Sulphate  of  soda,  or  glauber's  salt,  sulphate  of 
magnesia,  chloride  of  soda,  carbonate  of  soda  and  nitrate  of  soda 
may  be  found  as  constituents  of  soils  in  arid  sections,  and,  if 
present  in  excessive  quantity,  are  detrimental  to  vegetation  and 
give  rise  to  alkali  soils. 

Investigations  of  the  Mineral  Constituents  of  Soils. — Studies  of 
the  mineral  constituents  of  the  soil1  are  made  by  means  of  micro- 
scopic examination  with  the  aid  of  polarized  light,  stains,  and  other 
tests.  Comparatively  few  mineralogical  studies  of  the  soil  have 
been  made.  They  are  sufficient,  however,  to  show  that  there  are 
considerable  differences  in  the  mineral  content  of  soils,  particu- 
larly of  those  widely  different  origin. 

Chemical  examination  also  throws  some  light  upon  the  mineral 
1  Bull.  91,  Bureau  of  Soils. 


156  PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

composition  of  the  soil.  The  quantity  and  character  of  the  sub- 
stances brought  into  solution  by  means  of  various  solvents,  may 
be  compared  with  the  effect  of  the  same  solvents  under  the  same 
conditions  upon  minerals  in  the  proportions  in  which  they  may 
occur  in  soils.  For  example,1  known  phosphates  of  lime  are  com- 
pletely dissolved  by  fifth  normal  nitric  acid  under  certain  condi- 
tions ;  some  phosphates  of  iron  and  aluminium  are  also  completely 
dissolved,  while  basic  phosphates  of  iron  and  aluminium  are  dis- 
solved by  the  solvent  only  to  a  slight  extent.  Hence  treatment  of 
the  soil  with  this  solvent  gives  an  idea  as  to  the  condition  of  the 
inorganic  soil  phosphates.  This  matter  will  be  discussed  later. 
Hilgard2  determined  the  alumina  dissolved  and  the  silica  which 
was  liberated  by  strong  acids,  and  by  comparing  the  relative 
quantities,  came  to  the  conclusion  that  the  quantity  of  silica  was 
not  sufficient  to  combine  with  the  alumina  to  form  known  silicates, 
and  that  a  portion  of  the  alumina  in  certain  soils  is  present  as 
hydrated  alumina,  probably  Gibbsite  A1(OH)3. 

Organic  Matter. — The  organic  matter  and  nitrogen  of  the  soil 
are  closely  related,  for  nitrogen  is  chiefly  in  organic  combination. 
The  organic  matter  of  the  soil  consists  of  the  residues  of  plants 
and  animals,  animal  excremenls,  and  the  products  of  their  decay. 
All  the  compounds  which  are  found  in  plants  or  animals,  enter  the 
soil,  through  the  presence  of  some  of  them  is  very  transitory.3 
Sugars,  urea,  and  similar  substances,  are  rapidly  changed  into 
other  bodies.  Cellulose  and  lignin,  which  make  up  the  woody 
matter  of  plants,  decay  much  more  slowly,  and  may  remain  in  the 
soil  for  some  time.  Lactic,  acetic,  and  butyric  acids  are  pro- 
duced in  the  fermentation  of  sugars  and  starches.  Vegetable 
acids,  such  as  oxalic,  citric,  tartaric,  and  malic  acid  are  introduced 
into  the  soil  in  plant  residues,  but  are  quickly  destroyed  by 
bacteria.  Proteids  and  fats  persist  for  a  longer  or  shorter  time, 
according  to  their  nature.  It  is  thus  possible  for  all  the  organic 
compounds  found  in  plant  or  animal  residues  to  be  present,  in 

1  Texas  Station  Bulletin  126. 

2  The  Soil,  p.  389. 

8  Wollny,  Die  Zersetzung  d  Org.  Stoffe. 


CHEMICAL  CONSTITUENTS  OF  THK  SOII,  157 

greater   or  less   quantity,   in   the   soil,   and   the   student   of   soil 
chemistry  must  bear  this  possibility  in  mind. 

Organic  Compounds  Isolated. — Chemical  study  of  the  organic 
matter  of  the  soil  has  rendered  probable  the  existance  of  a  number 
of  organic  bodies  in  the  soil.  The  organic  compounds  claimed  to 
be  isolated,  so  far,  make  up  only  a  comparatively  small  percentage 
of  the  total  organic  matter. 

Schreiner  and  Shorey1  claim  to  have  isolated  sixteen  com- 
pounds. 

Hydrocarbons. — Hentriacontane  C3H64  from  a  North  Carolina 
soil. 

Acids. — Dihydroxystearic  acid  C1SH36O4  and  picoline  carboxylic 
acid  C3H7O,2H  from  several  soils.  Paraffinic  acid  C24H48O,,  and 
monohydroxystearic  acid  C18H36O3,  lignoceric  acid  C,4H48O.>, 
agroceric  acid  C21H42O2  and  resin  acids  from  individual  soils. 

Glycerides. — Glycerides  of  fatty  acids  identified  in  one  soil  and 
probably  present  in  several  soils. 

Wax  Alcohols. — Phytosterol  C26H44O.H2O  and  agrosterol 
C  CH44O.H2O  from  individual  soils. 

Nitrogenous  Compounds. — These  are  chiefly  bases,  and  form 
salts  with  acids.  Arginin,  cytosine,  xanthine,  and  hypoxanthine, 
were  claimed  to  be  isolated  from  several  soils. 

Pentosans. — The  presence  of  pentosans  in  the  soil  was  demon- 
strated by  de  Chalmot2  and  others  and  confirmed  by  Schreiner 
and  Shorey.  In  ten  soil  samples,  pentosan  carbon  made  up  1.30 
to  28.5  per  cent,  of  the  total  carbon. 

Ether  Extract? — The  soil  gives  up  about  0.02  per  cent,  material 
to  ether,  and  about  the  same  quantity  to  chloroform  following  the 
ether.  The  ether  extract  consists  of  fatty  acids  and  wax  alcohols, 
such  as  are  found  in  plants. 

Significance  of  the  Organic  Compounds. — As  stated  above,  the 
organic  compounds  mentioned  make  up  only  a  very  small  fraction 
of  the  total  organic  matter  of  the  soil.  The  bulk  of  the  organic  mat- 

1  Bulletins  53  and  74,  Bureau  of  Soils. 

2  Am.  Cliem.  Jour.,  1894,  p.  229. 
*  Texas  Bulletin,  157. 


158  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

ter  is  made  up  of  so-called  humus,  which  will  be  discussed  later. 
There  is  still  much  room  for  investigation  in  distinguishing  var- 
ious chemical  compounds  in  the  soil.  Some  of  the  organic  com- 
pounds mentioned  above  have  been  found  in  only  one  or  two  soils, 
while  others  are  perhaps  of  general  occurrence.  Most  of  them 
appear  to  be  indifferent  toward  plants,  and  their  significance  to- 
wards plant  growth  or  soil  chemistry  is  not  known.  The  import- 
ance of  these  substances  is  at  present  chiefly  due  to  their  relation 
to  the  toxic  theory  of  soil  fertility. 

The  Toxic  Theory. — According  to  the  toxic  theory  of  the 
Bureau  of  Soils,  "the  production  of  toxic  excretions  by  the 
roots  of  plants  is  undoubtedly  a  factor  in  soil  fertility."1  "So- 
called  exhausted  soils  are  poisoned  soils."2  "Practically  all  soils 
contain  sufficient  plant  food  for  good  crop  yields — and — this  sup- 
ply will  be  indefinitely  maintained."3  "The  small  yields  of  unpro- 
ductive soils  can  be  greatly  improved  by  treatments  which  destroy 
toxic  substances  in  these  soils."4  "The  soil  is  the  one  indestruct- 
ible immutable  asset  that  the  nation  possesses.  It  is  the  one  re- 
source that  cannot  be  exhausted,  that  cannot  be  used  up."5 

The  evidence  offered  in  support  of  this  theory  is  based 
chiefly  upon  experiments  in  water  cultures  and  wire-basket  tests 
of  about  three  weeks  duration.  The  aqueous  extract  from  an 
unproductive  soil  grew  larger  wheat  plants  when  ferric  hydrate, 
calcium  carbonate,  or  carbon  black  were  added  to  it.6  Pure  water 
is  better  suited  for  growing  wheat  plants  than  is  the  soil  extract 
of  poor  soils.7  The  extracts  of  the  poor  soils  are  benefited  by 
nitrate  of  soda,  carbon  black,  pyrogallic  acid  and  tannic  acid, 
and  the  same  chemicals  have  similar  effects  when  added  to  the 
soil.8  Dihydroxystearic  acid  and  picoline  carboxylic  acid  isolated 

1  Bulletin  40,  p.  40. 
'*  Bulletin  28,  p.  28. 

3  Bulletin  22,  p.  63  4. 

4  Bulletin  47,  p.  51. 

5  Bulletin  55,  p.  66. 

6  Bulletin  28. 
'  Bulletin  36. 
8  Bulletin  36. 


CHEMICAL  CONSTITUENTS  OF  THE)  SOIL  159 

from  soils  kill  wheat  seedlings  at  dilutions  of  100  parts  per 
million,  and  are  injurious  in  lower  amounts.1  Fertilizers  decrease 
the  injurious  effects  of  certain  organic  substances.2 

Dauheney/'  at  Oxford,  England,  tested  the  old  toxic  theory  of 
De  Condalle  by  a  rotation  experiment,  in  which  18  different  crops 
were  grown  continuously  on  the  same  plots  in  comparison  with 
the  same  crops  grown  in  various  rotations ;  the  yields  were  not 
sufficient  to  justify  the  assumption  of  the  existence  of  a  toxin. 
Russell4  grew  six  crops  of  rye  in  succession  on  sand  containing 


1 !  t 


J  3 


Fig.   37. — Wheat  seedlings  ten  days    old    grown    in  water  containing  di- 

hydroxystearic  acid  (i)  200  parts  per  million  ;   (2)  100  parts;  (3)  50 

parts  ;  (4)  20  parts  ;   (5)  o  parts.     Bureau  of  Soils. 

nutrient  salts.  A  seventh  crop  grown  on  this  sand,  and  another 
crop  on  fresh  sand,  were  practically  equal  in  size.  Other  experi- 
ments with  rye  on  soil,  and  with  buckwheat  and  spinach  on  sand 
and  on  soil,  give  practically  the  same  results.  Hence  there  is  no 
evidence  that  the  previous  crops  left  toxic  residues. 

1  Bulletin  47. 

2  Bulletin  70. 

3  Phil,  Trans.,  1845,  p.  179. 

4  Soil  Conditions  and  Plant  Growth,  p.  in. 


i6o 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Russell1  states  that  single  salts  of  potassium,  magnesium, 
sodium,  etc.,  are  toxic  to  plants,  in  water  culture,  while  a  mixture 
of  salts  is  not.  Breazeale  and  Le  Clerc2  show  that  wheat  seed- 
lings grown  in  culture  solutions  containing  10  parts  per  million  of 
potassium  chloride  or  potassium  sulphate,  cause  the  solution  to 
become  acid.  The  acidity  affects  injuriously  the  development 


go    on 


Fig.  38. — Wheat  seedlings  (second  crop)  grown  in,  (i)  distilled  water,  (2) 

distilled  water  and  calcium  carbonate,  (4)  potassium  sulphate 

and  calcium  carbonate,  compared  with  (3)  those  grown 

in  potassium  sulphate  solution. 


of  succeeding  plants  grown  in  the  solution,  and  a  similar  effect  is 
shown  by  solutions  of  sulphuric  acid  or  hydrochloric  acid. 
Sodium  hydroxide,  lime,  ferric  hydrate  or  carbon  black,  remove 
the  acidity  and  render  the  solution  less  injurious. 

1  Soil  Conditions  and  Plant  Growth,  p.  43. 

2  Bulletin  No.  149,  Bureau  of  Chemistry. 


CHEMICAL  CONSTITUENTS  OF  THE  SOIL  l6l 

There  is  thus  not  sufficient  experimental  evidence  to  support 
the  theory  that  low  yields  are  ordinarily  due  to  toxic  substances  in 
the  soil,  rather  than  to  deficiency  of  plant  food.  The  injurious 
effects  observed  in  the  water  culture  experiments  may  be  due  to 
acidity.  It  is,  of  course,  possible  that  some  soils  may  contain 
organic  toxic  substances  other  than  acids,  but  this  fact  has  not 
been  established. 

Assimilation  of  Organic  Compounds  by  Plants. — Experiments 
have  been  made  to  ascertain  whether  organic  compounds  may  be 
assimilated  by  plants.  The  organic  compounds  most  important 
are  those  which  may  enter  in  the  soil  in  animal  excrements 
or  plant  or  animal  residues,  or  may  be  formed  in  the  decay  of 
these.  Uric  acid  and  urea  are  found  in  urine,  hippuric  acid 
occurs  in  the  urine  of  cows,  sheep,  etc.,  leucin,  tyrosin  and 
asparagin,  are  found  in  plants  or  formed  in  their  decay.  Other 
organic  bodies  formed  in  the  decay  of  plants  or  animals,  are  prob- 
ably of  little  importance. 

The  question  as  to  the  assimilation  of  these  substances  as  such 
is  complicated  by  the  fact  that  they  are  for  the  most  part 'easily 
transformed  into  ammonium  salts,  which  may  be  assimilated. 

Baeyer  found  oats  to  grow  well  in  a  solution  of  urea,  and  the 
plants  contained  considerable  amounts  of  urea.  But  ammonia 
had  formed  in  the  solution.  Hampe1  grew  corn  with  urea  and 
found  the  leaves  to  contain  0.25  to  0.8 1  per  cent.  urea.  The 
solution  was  changed  every  day  to  avoid  error  by  decomposition, 
and,  though  the  corn  possibly  assimilated  some  ammonia,  the 
evidence  is  that  it  utilized  urea  also.  A.  Thomson2  compared 
sodium  urate,  sodium  hippurate,  urea,  and  sodium  nitrate,  on  oats 
and  barley  in  water  cultures,  and  found  that  uric  acid  and  urea 
have  the  same  value  as  nitric  acid,  but  hippuric  acid  has  not.  This 
investigator  did  not  correct  for  decomposition  of  the  compounds. 
Other  experiments3  could  be  quoted  tending  to  prove  that  leucin, 

1  Landw.  Versuchs-stat. ,  1867,  p.  79. 

2  Exp.  Station  Record  13,  p.  919. 

3  Hutchinson  and  Miller,  Jour.  Agr.  Sci.,  1912,  p.  283,  references  being 
given. 


l62  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

tyrosin,  asparagin,  and  hippuric  acid  can  serve  directly  as  sources 
of  nitrogen  for  cultivated  plants.  Hippuric  acid  is  decomposed 
into  glycocoll  and  benzoic  acid,  the  glycocoll  taken  up  and  the 
benzoric  acid  left  behind.  It  is  also  claimed  that  humic  acid1 
can  be  absorbed. 

Humus. — The  term  humus  is  applied  by  some  chemists  (prin- 
cipally in  European  countries)  to  the  entire  quantity  of  organic 
matter  in  the  soil,  in  whatever  form  it  may  be  present.  In 
America,  it  usually  refers  to  the  organic  matter  dissolved  by  am- 
monia after  the  lime  has  been  removed  by  acids.  This  ammonia- 
soluble  organic  matter  is  supposed  to  be  more  valuable  than  that 
not  soluble  in  ammonia,  though  satisfactory  evidence  that  such  is 
the  case  has  not  been  presented. 

Ammonia-Soluble  Organic  Matter. — In  the  preparation  of  the 
ammonia-soluble  organic  matter,  the  lime  is  first  extracted  with 
acid  and  the  soil  washed  free  from  acid.  The  soil  is  then  treated 
with  ammonia,  but  a  quantity  of  clay  is  also  suspended  in  the 
liquid.  The  clay  is  precipitated  by  addition  of  ammonium  sul- 
phate, ammonium  carbonate,  or  other  salts,  and  the  ammonia 
neutralized.  The  precipitate  is  collected  and  washed  thoroughly. 
The  precipitated  substance  is  a  black,  amorphous  body,  slightly 
soluble  in  water.  It  has  acid  properties.  It  decomposes  calcium 
carbonate,  liberating  carbon  dioxide.  A  portion  of  it  is  soluble 
in  alcohol.2  It  is  soluble  in  ammonia,  and  when  the  excess  of 
ammonia  is  evaporated,  retains  4  to  6  per  cent,  nitrogen  in  the 
form  of  an  ammonium  salt.  It  is  precipitated  by  salts  of  lime, 
barium,  copper,  zinc,  lead,  etc.,  forming  salts  of  these  metals.  Its 
combining  weight  varies  from  228  to  327.  The  magnesium  salt 
is  soluble  in  water,  and  also  the  sodium,  potassium  and  ammonium 
salts.  When  dissolved  in  ammonia,  a  portion  of  the  humate 
diffuses  through  parchment  paper. 

Analysis    of    the   substance   prepared    from    several    soils    by 

1  Brial,  Exp.  Sta.  Record  6,  p.  484. 

2  Fraps  and  Hamner,  Texas  Bulletin  129. 


CHEMICAL  CONSTITUENTS  OF  THE  SOIL  163 

precipitation  with  acid  from  ammonia  solution,  gives  the  follow- 
ing results  :l 

Per  cent. 

Carbon 44.09-63.58 

(usually  about  55  per  cent. ) 

Hydrogen 3-27~  5-45 

Nitrogen 3-36-  6.22 

Ash 1.57-15.74 

The  substance  is  probably  a  mixture  and  not  a  single  definite 
compound. 

According  to  Hilgard  and  Jaffa,2  the  humus  of  humid  soils 
(extracted  with  caustic  potash)  contains  about  5  to  5.5  per  cent, 
of  nitrogen,  while  that  of  arid  soils  may  contain  as  much  as  18.5 
per  cent,  nitrogen.  Hilgard  believes  that  the  nitrogen  content  of 
humus  should  not  fall  below  4  per  cent.,  if  the  soil  is  to  be  pro- 
ductive. 

Attempts  have  been  made  to  separate  definite  chemical  com- 
pounds from  humus,  the  success  of  which  is  doubtful.  Detmer3 
extracted  humus  from  the  soil  with  ammonia,  and  after  repeated 
purifications  obtained  a  compound  said  to  be  of  the  formula, 
C20H]8O9.  It  was  a  black  acid  substance  which  reddens  litmus, 
expels  carbonic  acid  from  carbonates,  and  forms  salts  with  lime, 
silver,  iron,  ammonia,  potassium,  etc.  These  salts  are  all  in- 
soluble with  the  exception  of  salts  of  the  alkalies.  Other  acids 
in  addition  to  this  one  are  claimed  to  have  been  separated  from 
the  soil.  There  is  doubt,  however,  whether  the  bodies  in  question 
are  really  definite  chemical  compounds  or  more  or  less  impure 
mixtures. 

There  is  no  evidence  that  the  ammonia-soluble  humus  of  the 
soil  consists  entirely  of  acids,  or  that  it  is  formed  by  decomposi- 
tion in  the  soil.  Various  bodies  known  to  be  non-acid  are  found  in 

1  Fraps  and  Hamner,  Texas  Station  Bulletin  129. 

'*  Rep.  Cal.  Exp.  Sta.,  189,  p.  2-4. 

3  Jahresber,  f.  Agr.  Chem.,  1870-2,  p.  68. 


164  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

plants,  such  as  proteids  and  lignin,  and  are  soluble  in  ammonia.1 
No  doubt  they  also  occur  in  the  soil.  In  attempts  to  determine 
the  formation  of  humus  in  the  soil,  these  ammonia-soluble 
materials  introduced  with  the  ingredients  have  been  neglected. 
In  experiments2  in  which  the  ammonia-soluble  organic  matter 
originally  in  the  soil  and  that  added  to  it,  were  estimated  before 
and  after  decomposition  for  several  months,  there  was  a  loss, 
and  not  a  gain,  of  ammonia-soluble  material.  The  following  is 
an  example  : 

Percentage  of  humus  in  original  soil 1.36 

Dry  soil  with  meat 2. 29 

Soil  with  meat  moist  for  14  weeks 1.68 

Estimation  of  Ammonia-Soluble  Humus. — In  the  estimation  of 
ammonia-soluble  humus,3  the  soil  is  first  extracted  with  I  per 
cent,  hydrochloric  acid,  to  remove  lime  and  decompose  the  com- 
pounds of  humic  acid.  It  is  then  washed  free  from  acid,  and 
treated  with  4  per  cent,  ammonia  for  some  time.  After  remain- 
ing in  contact  for  several  days,  the  solution  is  allowed  to  settle, 
and  an  aliquot  part  evaporated  to  dryness,  dried  and  weighed, 
ignited  and  weighed  again.  The  loss  in  weight  is  ammonia- 
soluble  humus. 

This  method  is  highly  inaccurate  on  account  of  the  presence  of 
clay.  Clay  will  remain  in  suspension  in  ammonia-water  for 
months,  and,  as  it  contains  chemically  combined  water,  will  lose 
weight  on  ignition,  after  drying.  It  is  also  present  in  the  humic  acid 
precipitated  with  the  solution,  unless  previously  removed.  The 
clay  may  be  easily  removed  by  precipitation  with  ammonium  car- 
bonate.4 The  ammonium  carbonate  is  volatilized  along  with  the 
ammonia  when  the  solution  is  subsequently  evaporated  to  dryness. 

Humus  of  Peat  and  Swamps. — As  we  have  already  stated,  acid 
bodies  are  formed  in  peat  and  muck  soils,  which  must  be 
neutralized  by  lime  before  the  soil  can  be  cultivated  profitably.  It 

1  Hoffmeister,  Landw.  Versuchs-stat.,  1898,  p.  347. 

2  Fraps  and  Hamner,  Texas  Bulletin  129. 

3  Methods  of  the  Association  of  Official  Agricultural  Chemists. 

4  Rather,  Bulletin  139,  Texas  Station. 


CHEMICAL  CONSTITUENTS  OF  THE  SOIL  165 

is  also  possible  that  the  lime,  by  combining  with  the  peat  resin, 
causes  the  peat  and  muck  to  oxidize  more  rapidly. 

Certain  investigators  claim  to  have  separated  ulmic  acid,  crenic 
acid,  and  other  acids  from  peat. 

Importance  of  Humus. — The  functions  of  the  organic  matter 
in  the  soil  may  be  summed  up  briefly  as  follows : 

1.  It  contains  the  store  of  nitrogen  of  the  soil. 

2.  It  furnishes  nutriment  for  bacteria  and  other  forms  of  life, 
which  aid  in  changing  plant  food  so  that  the  plant  can  take  it  up. 

3.  It  produces  carbon  dioxide  and  other  acids  in  its   decay, 
which  increase  the  solvent  action  of  the  soil  water  on  plant  food. 

4.  It  increases  the  retentiveness  of  sandy  soils  for  water,  and 
binds  the  fine  particles  of  clay  into  compound  particles,  so  that 
the  clay  has  better  tilth. 

5.  Like  lime,  an  abundance  of  humus  renders  a  soil  productive 
even  though  only  small  quantities  of  plant  food  are  present. 

Classification  of  Soils  with  Respect  to  Humus. — Knop1  makes 
the  following  divisions,  using  the  term  humus  to  mean  the  entire 
quantity  of  organic  matter  present : 

Per  cent. 

Poor  in  humus o.o  to    2.5 

Fair 2.5  to    5.0 

Good 5.0  to  10.0 

Rich 10.0  to  15.0 

Excess 15.0  and  over 

The  humus  in  the  soil  decreases  from  the  surface.  The  follow- 
ing analyses  by  Kosticheff  of  the  black  soil  of  Russia  illustrates 
this: 

Depth  Percentage 

inches  of  humus 

i  to    6 5.4 

6  to  12 4.8 

12  to  18 3.6 

18  to  24 2.6 

24  to  3c 2.6 

301036 1.9 

36to42 1.3 

1  Quoted  by  Wollny,  Zersetzung  d  Orgnanischen  Stoffe,  p.  192. 


1 66  PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

Ammonia-Soluble  Phosphoric  Acid. — The  ammonia-soluble  phos- 
phoric acid  of  the  soil  is  assumed  by  some  chemists  to  be  in  com- 
bination with  the  organic  matter  which  accompanies  it,  and  to  be 
of  considerable  value.  It  comes  in  part,  however,  from  inorganic 
phosphates  which  occur  in  the  soil  and  are  decomposed  by  am- 
monia, allowing  a  portion  of  their  phosphoric  acid  to  go  into  solu- 
tion.1 The  humic  acids  precipitated  with  acids  contain  a  small 
portion  of  the  ammonia-soluble  phosphoric  acid,  and  this  is  prob- 
ably in  organic  combination.  The  quantity  of  phosphoric  acid  held 
in  this  way  is  small,  even  in  soils  richly  supplied  with  humus.  It 
cannot  be  taken  up  until  released  by  oxidation  of  the  humus,  and 
can  only  be  regarded  as  a  reserve  store  of  phosphoric  acid,  not 
nearly  so  important  as  the  nitrogen  held  in  the  humus  in  much 
larger  proportion. 

1  Fraps,  Am.  Chem.  Jour.,  1898,  p.  574;  Bulletin  135,  Texas  Exp.  Sta. 


CHAPTER  IX. 


CHEMICAL  COMPOSITION  OF  THE  SOU. 

Chemical  analysis  shows  that  the  greater  bulk  of  the  soil 
is  composed  of  compounds  of  silica,  oxides  of  iron,  and  oxides 
of  alumina,  in  various  compounds.  These  substances  have  no 
value  as  plant  food,  except  iron,  and  only  very  small  amounts  of 
it  is  essential.  They  serve  a  useful  purpose,  however,  in  holding 
moisture,  modifying  the  supply  of  plant  food,  supporting  the 
plant,  and,  giving  it  a  medium  in  which  to  develop  its  roots. 

The  important  plant  foods — nitrogen,  phosphoric  acid,  and 
potash —  make  up  only  a  small  percentage  of  the  soil.  The 
quantity  of  plant  food  may  be  large  in  pounds  per  acre,  sufficient 
for  several  hundred  crops,  if  it  were  all  available  for  use  of  the 
plant.  But  the  proportion  of  plant  food  to  the  total  quantity  of 
soil  is  small.  Further,  the  amount  which  can  be  taken  up  by 
plants  may  be  only  a  small  proportion  of  the  total  amount  pres- 
ent ;  so  that  although  several  hundred  pounds  of  phosphoric  acid, 
for  instance,  may  be  present  in  the  soil,  the  addition  of  a  few 
pounds  of  highly  available  phosphoric  acid  may  produce  a  large 
increase  in  the  crop. 

Methods  of  Examination. — Four  chief  methods  of  examining 
soils  have  been  used.  In  addition,  special  methods  are  used  for 
special  analyses. 

(1)  Complete    decomposition   of   the   silicates.     This   method 
gives  the  total  quantity  of  the  constituents  of  the  soil. 

(2)  Partial    decomposition    with    strong   acid.     This    method 
attempts  to  determine  the  quantity  of  plant  food  which  may  be- 
come available  to  the  plant  in  a  series  of  years.     It  distinguishes 
between  the  most  resistant  silicates,  and  those  decomposed  by 
acids. 

(3)  Weak  Solvents.     This  method  attempts  to  determine  the 
immediate  needs  of  the  soil  for  plant  food. 

(4)  Water-Soluble  Constituents.     This  method  considers  the 
material  extracted  from  the  soil  by  water. 


i68 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Complete  Decomposition. — The  complete  analysis  of  the  soil 
ib  made  in  two  ways: 

First  Method. — The  soil  is  fused  with  a  mixture  of  sodium 
carbonate  and  potassium  carbonate.  The  silica  unites  with  the 
soda  or  potash,  forming  silicates ;  oxides  or  carbonates  are 
formed  from  the  bases.  On  treatment  with  water  and  acids,  the 
carbonates  and  oxides  dissolve.  The  silica  can  easily  be  separated 
and  the  bases  determined  in  the  solution.  If  potash  or  soda  is 
to  be  estimated,  they  must  be  brought  into  solution  by  some  other 
method,  such  as  that  named  below,  or  by  fusing  the  silicate  with 
lime. 

Second  Method. — The  soil  is  treated  with  hydrofluoric  acid, 
until  the  silicate  is  completely  dcomposed  and  the  silica  driven 
off  as  gaseous  silicon  fluoride  SiF4.  The  residue  is  then  dis- 
solved in  acids,  and  subjected  to  analysis.  The  estimation  of  the 
silica,  if  desired,  is  accomplished  by  the  first  method. 

Complete  decomposition  of  a  soil  shows  the  constituents  which 
are  locked  up  in  the  most  refractory  silicates,  as  well  as  those 
which  are  easily  affected  by  plants.  So  far  as  the  writer  has  been 
able  to  find,  there  have  been  no  investigations  made  as  to  the 
relation  of  the  complete  analysis  of  the  soil  to  its  wearing 
qualities,  or  needs  for  plant  food.  The  utmost  information  such 
analysis  provides  at  present,  is  the  amount  of  plant  food  which 
may  some  day  become  available. 

The  complete  analysis  of  some  groups  of  soils  is  shown  in  the 
following  table,  compiled  from  Bulletin  No.  54  of  the  Bureau  of 
Soils : 

COMPLETE  COMPOSITION  OF  SOME  SOIL  GROUPS,  PER  CENT. 


No. 
averaged 

P205 

CaO 

MgO 

KoO 

o  16 

"D  pel  filial 

o  18 

o  67 

o  -6 

*••// 

2  08 

Glacial            

jO 

O  22 

i  ^ 

o  80 

O  27 

o  86 

2.Uy 
2  go 

Relation  to  Sizes  of  Particles. — Chemical  analysis  of  the  differ- 
ent grades  of  particles  have  not  always  given  the  same  result,  but 


CHEMICAL  COMPOSITION  OF  THE  SOIL 


169 


as  a  rule,  the  percentages  of  alumina,  potash,  and  lime  increases 
as  the  size  of  the  particles  decrease.  For  example,  Failyer1 
determined  phosphoric  acid,  lime,  magnesia,  and  potash  in 
separate  grades  of  particles  from  a  number  of  soils  of  the  United 
States  by  the  method  of  complete  decomposition.  In  the  follow- 
ing table  is  given  the  average  percentage  of  three  ingredients  of 
the  sand,  silt,  and  clay  of  four  groups  of  soils : 


Phosphoric  acid 

Ivime 
Silt 

Clay 

Potash 

Sand 

Silt 

Clay 

Sand 

Sand 

Silt 

Clay 

7  Coastal  plains  so^s 

0.03 
0.07 

0.15 
0.04 

O.IO 
O.2I 
0.23 
O.O7 

0-34 
0.67 
o'.86 
o.  16 

0.07 
0.50 
1.24 
1.  80 

0.19 
0.82 
1.30 

1.88 

0-55 
0.94 
2.68 
2.85 

32 

1.72 

0.18 

1-33 
2-37 
2-35 
i.  02 

1.76 
2.86 
3-o8 
0.84 

jo  Glacial  soils  

5  Limestone  and  shale  soils.  . 

It  is  seen  that  the  finer  particles  of  the  soil  are,  on  an  average, 
richer  in  phosphoric  acid,  lime,  and  potash  than  are  the  coarser 
particles.  The  percentage  of  each  of  the  constituents  named 
increases  with  the  fineness  of  the  particles,  the  only  exception  in 
the  table  being  the  potash  in  the  clay  of  the  limestone  and  shale 
soils.  The  relative  abundance  of  the  various  grades  of  particles 
would  determine  the  quantity  which  each  contributes  to  the1  soil. 
The  coastal  plains  soils  have  been  so  weathered  and  leached,  that 
they  are  lower  in  phosphoric  acid,  lime,  and  potash  than  the  less 
extensively  weathered  residual  soils,  and  these  in  turn  are  lower 
than  the  glacial  soils,  which  consist  largely  of  crushed  rocks,  many 
of  which  have  not  been  weathered  to  a  great  extent. 

Analysis  by  Extraction  with  Strong  Acids. — This  is  the  method 
usually  employed  in  the  analysis  of  the  soil.     It  consists  in  treat- 
ing the  soil  with  strong  acid  and  estimating  the  constituents  which 
go  into  solution.     The  extent  of  the  solvent  action  depends  upon 
the  nature  of  the  soil,  the  kind  of  acid,  strength  of  acid,  tempera- 
ture, time  of  contact,  and  ratio  of  soil  and  acid.     The  methods 
used  by  different  chemists  vary.     In  the  methods  of  the  Asso- 
ciation   of    Official    Agricultural    Chemists    of    North    America 
1  Bulletin  54,  Bureau  of  Soils. 
12 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


10  grams  soil  are  digested  with  100  cc.  hydrochloric  acid 
of  1.115  specific  gravity  for  8  hours  at  the  boiling  tem- 
perature. Dr.  E.  W.  Hilgard  digests  the  soil  on  the 
steam  bath  for  five  days,  a  method  which  appears  to  give 
nearly  the  same  results  as  the  official  method,  with  the  exception 
of  potash,  and  oxides  of  iron  and  alumina.  In  the  one  comparison 
made  by  Dr.  Loughridge,1  0.35  per  cent,  potash  was  dissolved  by 
the  one  method,  and  0.63  per  cent,  by  the  other,  or  nearly  twice 
as  much.  This  difference  must  be  considered  in  comparing  the 
analyses  made  by  Hilgard's  method  with  the  analyses  made  by  the 
methods  of  the  Association  of  Official  Agricultural  Chemists. 

The  proportion  of  the  constituents  of  the  soil  which  are  dis- 
solved by  strong  hydrochloric  acid  varies  considerably  with  differ- 
ent soils.  For  example,  Veitch2  determined  in  16  Maryland  soils 
the  total  quantity  of  each  constituent  and  the  quantity  dissolved 
by  strong  acid  by  the  A.  O.  A.  C.  method.  The  results  are  pre- 
sented in  the  following  table,  expressed  in  percentage  of  the  total 
quantity  of  each  ingredient  present : 

PERCENTAGE  OF  TOTAL  PHOSPHORIC  ACID,  ETC.,  DISSOLVED  BY 
STRONG  ACIDS. 


• 

Average 

Minimum 

Maximum 

6l 
I? 
35 
56 
54 
82 

32 
5 
10 
10 
24 
57 

100 
33 
77 

100 
IOO 
IOO 

Potash 

The  average  order  in  which  the  constituents  of  these  soils  were 
dissolved  was  as  follows,  beginning  with  the  most  soluble:  oxide 
of  iron,  phosphoric  acid,  magnesia,  alumina,  lime,  and  potash.  On 
an  average,  only  17  per  cent,  of  the  total  potash  of  the  soil  was 
dissolved  by  the  A.  O.  A.  C.  method.  None  of  the  soils  in  ques- 
tion were  highly  calcareous,  otherwise  a  much  greater  proportion 
of  lime  and  magnesia  would  have  been  dissolved. 

1  Hilgard,  The  Soil,  p.  341. 

2  Maryland  Bulletin  No.  70. 


CHEMICAL  COMPOSITION  OF  THE)  SOIL 


Relation  of  Composition  to  Fertility. — The  relation  of  the  com- 
position to  the  fertility  of  the  soil  is  studied  by  comparing  the 
chemical  analysis  with  the  productiveness  of  known  soils. 

Soils  containing  comparatively  high  quantities  of  plant  food 
are  generally  very  productive  and  durable,  under  favorable 
physical  conditions.  The  following  table  shows  the  composition 
of  some  very  productive  soils.1  These  soils  are  all  well  known 
for  their  fertility  and  wearing  qualities. 

PERCENTAGE  COMPOSITION  OF  FERTILE  SOILS. 


California 
Arroyo  Grande 
Valley 

Mississippi 
Yazoo  Bottom 

Texas 
Rio  Grande 
Bottom 

Russia 
Tchernozen 

Phosphoric  acid  

O7I 

Potash    . 

L/itne  •  •  •  • 

•31 

0.72 

Magnesia  

2  ofi 

167 

14-43 

I-5I 

Carbon  dioxide  

I  82 

l.O/ 

•53 

°-73 

Sulphur  Trioxide  .... 

•91 

Alumina  

Oxide  of  iron  

JU-04 

c   Q2 

.11 

.22 

Insoluble    and   soluble 
Silica  

•*O 

72  A1 

o-°^ 

71   77 

4-uy 

.12 

6  61 

/*•// 

717 

22   78 

•01 

^./O 

The  Arroyo  Grande  Valley  soil  is  considered  one  of  the  richest 
soils  in  the  world.  The  other  soils  mentioned  in  the  table  are  all 
productive  and  durable.  The  analyses  were  made  by  Hilgard's 
method.  Soils  containing  about  I  per  cent,  lime,  0.15  per  cent, 
phosphoric  acid,  and  I  per  cent,  potash,  by  Hilgard's  method,  may 
be  regarded  as  highly  fertile.  The  same  standards  apply  to  the 
Association  method,  excepting  it  is  possible  that  0.50  per  cent, 
potash  is  sufficient  for  a  fertile  soil.  This,  however,  remains  to  be 
demonstrated. 

When  soils  contain  only  small  quantities  of  plant  food,  they 
will  usually  be  found  deficient  in  plant  food  for  crops,  or  become 
so  in  a  comparatively  short  time  after  being  placed  in  cultivation. 
It  appears  probable  that  the  plant  food  which  can  be  taken  up  by 

1  Hilgard,  The  Soil,  p.  343. 


172 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


plants  is,  to  a  large  extent,  proportional  to  the  total  quantity 
present,  though  this  depends  on  the  changes  going  on  in  the  soil. 

A  comparatively  small  amount  of  plant  food  in  the  soil  is 
sufficient  to  make  it  productive,  if  present  in  an  available  form. 
If  we  assume  the  weight  of  one  acre  of  soil  to  the  depth  of  one 
foot  to  be  $y2  million  pounds,  then  o.oi  per  cent,  corresponds  to 
350  pounds  per  acre  foot.  A  crop  of  40  bushels  of  corn,  including 
ears,  stalk  and  leaves,  requires  about  25  pounds  phosphoric  acid, 
which  would  be  about  0.0007  per  cent.,  or  7  parts  per  million.  Con- 
sequently as  much  as  o.oi  per  cent,  phosphoric  acid  could  supply 
14  crops  of  corn  of  this  size,  if  the  plant  could  get  it.  But  soils 
containing  only  this  quantity  of  phosphoric  acid  usually  respond 
to  applications  of  phosphoric  acid  greatly. 

The  analysis  by  strong  acids  does  not  differentiate  between  com- 
pounds which  may  have  different  values  to  crops.  Hence  two 
soils  may  have  the  same  composition  but  react  differently  to 
fertilizers.  The  chemical  composition  as  determined  in  this  way, 
is  more  closely  related  to  the  wearing  qualities  of  the  soil  than  to 
the  immediate  needs  of  the  soil  for  plant  food. 

Number  of  Crops  the  Plant  Food  Will  Supply. — This  depends 
on  the  size  and  kind  of  crop,  as  well  as  on  the  composition  of  the 
soil,  Assuming  the  entire  removal  of  a  crop  of  40  bushels  corn 
per  acre,  the  following  is  the  number  of  crops  which  could  be 
supplied  by  the  acid-soluble  phosphoric  acid  and  potash,  and  the 
total  nitrogen  in  some  Texas  soil  types,1  if  they  were  in  such 
forms  that  they  could  be  used  by  the  crops  without  any  loss. 


Corn 

Number  of  crops  the  plant  food  will  supply 

Phosphoric 
acid 

Nitrogen 

Potash 

28 
70 
28 
42 
84 
154 

29 

35 
29 

4i 
82 
56 

IOO 
308 
91 
I83 
290 

325 

Bulletin  126,  Texas  Station  ;  see  also  No.  99. 


CHEMICAL  COMPOSITION  OF  THE  SOIL  173 

Interpretation  of  Partial  Soil  Analyses. — The  chemical  analysis 
of  a  soil  must  be  considered  in  connection  with  a  knowledge  of  its 
location,  depth,  drainage  conditions,  permeability  to  water  and 
air,  and,  if  possible,  the  amount  of  crops  it  produces.  Without 
consideration  of  the  other  factors  which  influence  the  fertility  of 
a  soil,  the  chemical  analysis  may  not  lead  to  satisfactory  con- 
clusions. We  must  also  remember  that  the  same  general  type  of 
soil  varies  somewhat  in  composition,  physical  properties,  and  pro- 
ductiveness within  a  given  area,  and  also  that  different  methods 
of  farming  may  cause  considerable  differences  in  soils  originally 
the  same. 

The  interpretation  of  a  chemical  analysis  unaccompanied  by 
knowledge  of  the  other  soil  conditions  which  affect  its  fertility, 
may  be  unsatisfactory  in  a  large  proportion  of  cases.  A  careful 
interpretation  of  results  with  the  aid  of  the  knowledge  referred  to 
may  sometimes  be  disappointing,  but  it  is  more  often  correct. 
Analyses  of  miscellaneous  samples  of  soils  is  also  of  less  value 
than  systematic  studies  of  definite  areas.  Analyses  of  virgin 
soils,  or  soils  which  have  not  been  long  under  cultivation,  or  not 
treated  with  fertilizers,  are  more  likely  to  yield  a  satisfactory 
interpretation  than  analyses  of  soils  whose  properties  have  been 
modified  by  long  continued  cultivation,  or  by  applications  of 
fertilizers.  It  cannot  be  expected  that  chemical  analysis  of  soils 
will  always  give  a  satisfactory  interpretation ;  there  will  be 
exceptions  which  may  be  difficult  to  understand  until  the  scope  of 
our  information  has  been  widened. 

Chemical  analysis  of  a  soil  with  strong  acids,  together  with 
other  information  concerning  the  soil,  should  aid  us  in  applying 
the  results  secured  by  field  experiments  in  one  locality  on  a  given 
type  of  soil,  to  other  localities  and  to  other  types  of  soil.  It  is 
well  known  that  the  results  of  field  experiments  with  fertilizers 
are  applicable  only  to  the  same  types  of  soils  under  similar  con- 
ditions and  with  similar  chemical  composition,  and  may,  or  may 
not,  be  applicable  to  other  types  of  soils.  Chemical  analysis,  and 
the  other  information  referred  to,  should  aid  us  in  applying 
knowledge  secured  by  field  experiments  and  by  experience,  to  the 


174  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

same  type  of  soils  located  in  different  sections,  and  even  to  differ- 
ent types  of  soil  from  those  under  experiment. 

The  analysis  of  a  soil  with  strong  hydrochloric  acid  does  not 
show  exactly  what  fertilizer  to  apply  to  it,  but  it  does  give  indica- 
tions (a)  as  to  the  wearing  qualities  of  the  soil,  (b)  what  elements 
are  likely  to  become  deficient  first  under  a  given  system  of 
cropping,  (c)  what  deficiencies  already  exist  in  the  soil,  or  will 
soon  be  brought  out. 

Virgin  soils  containing  high  percentages  of  plant  food  are 
highly  productive  unless  improper  physical  conditions  interfere 
with  the  welfare  of  the  plant.  Low  percentages  of  plant  food  do 
not  necessarily  indicate  low  production  when  first  put  in  cultiva- 
tion. To  use  Hilgard's  illustration,  suppose  a  heavy  alluvial  soil 
of  high  plant  food  content  is  diluted  with  its  own  weight  of  sand. 
By  improving  the  physical  condition  of  the  soil  an  increased  crop 
will  very  likely  result,  though  the  percentage  of  plant  food  has 
been  reduced  by  half.  The  root  system  of  the  plant  in  the  diluted 
soil  will  probably  be  better  developed  and  in  more  intimate  contact 
with  the  soil  particles,  than  in  the  undiluted  soil.  We  may  con- 
tinue the  dilution,  using  say  4  parts  of  sand  to  one  of  soil,  6  parts 
of  sand  to  one  of  soil,  and  so  on.  At  some  point,  the  size  of  the 
crop  will  begin  to  decrease  on  account  of  the  difficulty  of  secur- 
ing plant  food.  How  far  the  dilution  may  be  carried  depends 
upon  the  plant  and  on  the  soil,  and  is  a  subject  worthy  further 
study. 

Standards  for  Interpretation. — Varying  methods  of  analysis 
for  soils,  and  varying  standards  of  interpretation  are  used  accord- 
ing to  the  method  of  analysis  and  the  individual  opinions  of  the 
analysts  as  to  what  constitutes  a  good  soil.  The  standards  of 
Hilgard1  are  based  upon  a  large  number  of  analyses  and  wide 
observation,  and  appear  well  adapted  to  American  conditions. 
These  standards  give  best  results  when  applied  to  virgin  soils. 

Phosphoric  Acid. — Hilgard  states  that  phosphoric  acid  is 
seriously  deficient  in  virgin  soils  when  below  0.05  per  cent.,  unless 
accompanied  by  a  large  amount  of  lime.  In  heavier  virgin  soils, 
1  Tenth  Census  of  the  U.  S. 


CHEMICAL  COMPOSITION  OF  THE  SOU, 


175 


o.i  per  cent,  phosphoric  acid,  when  accompanied  by  a  fair  amount 
of  lime,  secures  fair  productiveness  from  eight  to  fifteen  years; 
with  a  deficiency  of  lime,  twice  the  percentage  will  only  serve  for 
a  similar  time.  Soils  containing  between  o.i  and  0.05  per  cent, 
of  phosphoric  acid  are  considered  as  likely  to  respond  to  fertiliza- 
tion with  phosphates  in  a  short  time.  A  large  supply  of  organic 
matter  appears,  like  a  large  supply  of  lime,  to  offset  a  deficiency  in 
phosphoric  acid.  Large  quantities  of  hydrated  ferric  oxides  may 
render  even  large  quantities  of  phosphoric  acid  inert  and  unavail- 
able to  plants. 

Lime. — Lime  is  exceedingly  important  to  the  soil.  Low 
percentages  of  potash,  phosphoric  acid,  and  potash  are 
adequate  when  a  large  proportion  of  lime  carbonate  is  present. 
Many  of  our  richest  soils  are  calcareous  soils,  such  as  the  blue- 
grass  soils  of  Kentucky,  the  black  prairie  soils  of  Mississippi  and 
Texas,  the  calcareous  prairie  soils  of  Illinois,  Indiana,  and  Iowa. 
These  soils  are  productive  and  durable. 

Heavy  clay  soils  with  less  than  0.5  per  cent,  of  lime  do  not, 
according  to  Hilgard's  observation,  carry  the  plants  characteristic 
of  calcareous  soils.  The  lightest  sandy  soil  should  not  contain 
less  than  o.io  per  cent,  of  lime;  clay  loams  should  contain  0.25 
per  cent.  There  is  no  advantage  in  more  than  2.00  per  cent.  It 
appears  that  an  excess  of  potash  may  offset  deficiency  of  lime. 

The  following  examples1  show  the  effect  of  lime  in  overcoming 
a  deficiency  in  phosphoric  acid : 


A 

B 

C 

D 

0.068 
1.254 
0.366 

0.033 

I-37I 
0.699 

0.030 
0.129 
0.259 

0.038 
0.034 

0.218 

Potash                       

Soils  A  and  B  were  highly  productive,  falling  off  suddenly  at 
the  end  of  15  or  20  years.  Soils  C  and  D  scarcely  produced  500 
pounds  seed  cotton  per  acre  when  fresh,  and  then  only  for  three 
or  four  years.  The  difference  appears  to  be  due  to  an  abundance 
of  lime  in  the  first  two,  a  deficiency  in  the  second  two. 
1  Tenth  U.  S.  Census. 


176 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


E 

F 

G 

0.411 
0.197 
0.422 

0.188 
0.047 
0.178 

o  042 

0.286 
0-334 

Potash                        •  *  • 

Soil  E  with  a  very  high  percentage  of  phosphoric  acid  and  only 
a  moderate  supply  of  lime,  is  very  productive.  Soils  F  and  G 
the  one  with  fair  lime  and  low  phosphoric  acid,  the  other  with 
the  proportions  reversed,  are  both  about  equally  productive. 

Potash. — According  to  Hilgard,  sandy  soils  of  great  depth  may 
contain  less  than  o.io  per  cent,  potash  without  being  deficient 
therein;  sandy  loams  contain  0.3  to  o.i  per  cent.;  loams  0.45  to 
0.3  per  cent.,  heavy  clays  and  clay  loams  o.8c  to  0.45  per  cent. 
As  a  rule,  soils  containing  less  than  0.25  per  cent,  potash  are 
likely  to  require  fertilization  with  potash  salts  early,  while  as 
much  as  0.45  per  cent,  seems  to  be  sufficient  for  the  same  soils. 
Sometimes,  however,  a  soil  rich  only  in  lime  and  phosphoric  acid 
shows  good  productiveness  despite  a  low  potash  percentage,  and 
conversely  a  high  percentage  of  potash  may  offset  a  low  per- 
centage of  lime. 

The  availability  of  the  potash  depends  upon  the  general  char- 
acter of  the  soil.  With  a  good  supply  of  available  lime  and 
magnesia,  the  potash  of  the  soil  is  usually  in  an  available  form. 

The  above  standards  are  for  potash  estimated  according  to 
Hilgard's  method.  The  Association  method  dissolves  less  potash 
and  calls  for  lower  standards.  Exactly  what  these  standards 
should  be,  remains  to  be  determined. 

Nitrogen. — Nitrogen  is  present  in  the  soil  in  organic  compounds 
which  cannot  be  taken  up  by  plants,  and  which  change  slowly  into 
compounds  which  can  be  assimilated.  This  change  depends 
largely  upon  physical  conditions,  though  the  composition  and 
nature  of  the  soil  also  have  an  influence.  The  rapidity  of  the 
production  of  active  plant  food  is  more  important  than  the 
quantity  of  nitrogen.  It  is  thus  evident  that  it  is  difficult  to  fix 
a  standard  for  nitrogen.  It  has  generally  been  assumed  that  o.io 
per  cent,  is  adequate.  With  less  than  0.07  per  cent,  the  soil  is 


CHEMICAL  COMPOSITION  OF  THE  SOIL 


177 


usually  deficient.     Lime,  as  with  other  plant  foods,  also  has  an 
influence. 

Examples  of  Interpretations  of  Soil  Analyses. — The  following 
examples  are  taken  from  Hilgard1.  See  accompanying  table. 

Soils  No.  i  and  No.  2  are  highly  productive,  and  No.  3  is  a 
very  good  soil.  There  is  a  great  difference  in  the  chemical  com- 
position. No.  i,  however,  is  a  heavy  clay  soil,  while  Nos.  2  and 
3  are  sands,  and  hence  need  to  contain  less  plant  food.  Plant 
roots  can  also  exercise  their  functions  to  the  depth  of  three  or 
four  feet  in  them,  while  in  soil  No.  i,  the  roots  rarely  reach  below 
12  or  15  inches.  Soils  No.  4  and  5,  almost  worthless,  are  deficient 
in  phosphoric  acid,  and  No.  4  is  also  deficient  in  lime.  In  addi- 
tion, these  soils  are  underlaid  by  an  almost  pure  sand  at  the  depth 
of  12  inches.  These  facts  are  sufficient  explanation  of  their 
character. 

PERCENTAGE  COMPOSITION  OF  SOILS. 


No.    i 

stiff 
buckshot 
soil,  highly 
productive 

No.   2 

Very  sandy, 
highly 
productive 

No.  3 

Sandy  soil, 
medium  pro- 
ductiveness 

No.  4 

Gray  sand, 
almost 
worthless 

No.  5 

Gray  sand, 
almost 
worthless 

Phosphoric  acid  .  .  . 
Lime   

0.30 

O.o8 

0.  10 

0.02 

0.03 

Potash  

1-oo 

I    IO 

•J3 

<_>.  13 

•25 

No.  6 

Stiff  red 
soil,  fairly 
productive 

No.  7 

Stiff  black 
prairie,  very 
productive 

No.  8 

Stiff  soil, 
practically 
worthless 

No.  9 

Stiff  black 
prairie,  very 
productive 

No.  10 

Stiff 
flatwood 
inferior 
quality 

Phosphoric  acid  •  •  . 

0.19 

0.03 

O.o6 

O.  IO 

0.05 
r»  T£ 

Potash  •  . 

U-O4 

•o/ 

I-73 

n  iS 

u-4o 

•53 

0.30 

°-75 

Soils  Nos.  6  to  10  exhibit  the  effect  of  lime  on  the  character  of 
the  soil ;  soils  7  and  9  being  rich  in  lime,  the  others  being  poor 
in  this  ingredient.  Soils  7  and  9  are  very  productive.  Soil  7 
shows  the  effect  of  a  large  amount  of  lime  in  overcoming  a 
deficiency  in  phosphoric  acid,  soils  6,  8  and  10,  with  more  phos- 
1  Tenth  U.  S.  Census. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


phoric  acid,  being  much  poorer  soils.  Soil  6  is  fairly  productive 
in  good  seasons,  soil  8  is  considered  practically  worthless,  and 
soil  10  is  of  inferior  quality . 

Iron  and  Alumina. — The  percentage  of  alumina  is  an  imperfect 
indication  of  the  amount  of  clay  in  the  soil.  Enough 
silica  seldom  dissolves  to  satisfy  the  requirement  for  combining 
with  alumina  to  form  kaolinite.  The  percentage  of  alumina 
extracted  is  always  larger.  In  numerous  cases  so  little  silica 
is  present  as  to  raise  a  question  as  to  the  form  of  alumina  in  the 
soil,  the  hydrate  (Gibbsite)  being  almost  the  only  possible  one, 
aside  from  zeolitic  minerals. 

From  1.5  to  4  per  cent,  are  ordinary  percentages  of  ferric  oxide, 
occurring  even  in  soils  but  little  tinted.  Ordinary  ferruginous 
loams  vary  from  3.5  to  7  per  cent. ;  highly  colored  red  lands  have 
7  to  12  per  cent,  ferric  oxide  and  occassionally  20  per  cent,  or 
more.  Since  highly  ferruginous  soils  rarely  have  a  high  per  cent, 
of  humus,  it  appears  that  the  iron  acts  as  a  carrier  of  oxygen,  and 
this  probably  favors  oxidation. 

Relative  Composition  of  Soils  of  Arid  and  Humid  Regions.— 
Hilgard1  has  compiled  a  great  number  of  analyses  of  soils  of  arid 
and  humid  regions,  made  with  strong  acid,  with  the  result  that 
the  soils  of  the  arid  region  are  found  to  be,  on  an  average, 
richer  in  plant  food  and  in  lime,  than  soils  of  the  humid  region. 
Arid  soils  are  prevailingly  calcareous,  while  humid  soils  are 
siliceous.  This  may  be  in  large  part  due  to  the  fact  that  the  con- 

PERCENTAGE  COMPOSITION  OF  SOILS  OF  ARID  AND  HUMID  REGIONS. 


Humid, 
average  of 
696  analyses 

Arid, 
average  of 
573  analyses 

0.12 
0.21 
O.I3 
0.29 
005 

3.66 
3-88 
88.21 
4.40 

0.16 
0.67 

i-43 
1.27 
0.06 
7.21 
5-48 
75.87 
5-15 

PntfmVi 

T  imp 

1 

1  Bulletin  No.  3.  U.  S.  Weather  Bureau. 


CHEMICAL  COMPOSITION  OF  THE  SOIL 


179 


tinued  leaching  of  the  soils  in  humid  regions  washes  out  the  plant 
food.  It  may  also  be  partly  due  to  the  difference  in  origin,  as 
many  of  the  humid  soils  are  coastal  deposits  worn  by  the  water, 
while  many  soils  in  the  arid  region  are  comparatively  new  soils 
from  igneous  rocks. 

Soils  and  Subsoils. — If  we  compare  the  composition  of  soils 
with  the  corresponding  subsoil,  we  find,  almost  always,  that  the 
subsoil  contains  less  nitrogen  than  the  surface  soil.  It  often  con- 
tains more  potash,  more  oxide  of  iron  and  alumina,  and  less  in- 
soluble material,  than  the  surface  soil.  This  difference  is  largely 
due  to  the  percolating  water  carrying  the  finer  particles  of  the 
soil  (clay)  into  the  subsoil.  There  is,  however,  a  good  deal  of 
difference  in  soils  in  this  respect. 

Relation  of  Composition  to  Type. — Soils  of  different  type  differ 
to  some  extent  in  chemical  composition,  though  such  is  not  in- 
variably the  case.  There  is  also  some  variation  in  individual 
members  of  the  type.  Differences  in  composition  are  usually 
accompanied  by  differences  in  properties,  productiveness  or  value 
of  the  soil. 

AVERAGE  PERCENTAGE  COMPOSITION  OF  SOME  TYPICAL  TEXAS  SOILS. l 


Phos- 
phoric 
acid 

Nitro- 
gen 

Potash 

Lime 

Mag- 
nesia 

O.O2 
O.O2 
O.O2 
0.04 
0.08 
0.08 
O.OI 

0.09 
0.04 
0.04 

O.o6 
O.O2 
O.O4 
O.o6 
O.O9 
O.O7 
O.O7 
0.13 
0.12 
O.I  I 

0.09 
0.08 
O.I  2 
0.12 
O/62 
0.63 
O.T2 

0.88 
0.25 
0.40 

0.08 
0.06 

O.I  I 

0.14 

O.20 
0.12 

0.51 

0.03 
O.o6 
0.92 
0.16 

0-35 
0.09 

0.40 

Susquehanna  fine  sandy  loam  (3  samples)  .  • 

Orangeburg  fine  sandy  loam  (6  samples)  .  . 

Detailed  analyses  and  discussion  of  the  soils  of  the  United 
States  are  to  be  found  in  Bulletin  57  of  the  Bureau  of  Soils,  and 
in  "Soil  Fertility  and  Permanent  Agriculture"  by  C.  G.  Hopkins. 
1  Bulletin  126,  Texas  Station. 


CHAPTER  X. 


ACTIVE  PLANT  FOOD  AND  WATER-SOLUBLE  CONSTITUENTS 
OF  THE  SOIL. 

The  complete  analysis  of  the  soil,  or  its  partial  analysis  by 
strong  acids,  does  not  show  clearly  the  immediate  needs  of  the  soil 
for  plant  food.  Various  weak  solvents  have  been  used  for  this 
purpose,  with  some  measure  of  success. 

Active  plant  food  is  a  term  used  to  designate  the  potash  and 
phosphoric  acid  soluble  in  fifth-normal  nitric  acid.  We  are  not 
yet  able  to  ascribe  different  values  to  the  organic  nitrogen  com- 
pounds of  the  soil. 

Dilute  Citric  Acid. — Numerous  attempts  have  been  made  to 
ascertain  soil  deficiencies  by  means  of  weak  solvents,  such  as 
water,  water  containing  carbon  dioxide,  weak  solutions  of  citric, 
hydrochloric,  nitric,  or  oxalic  acids,  etc. 

Dyer1  found  that  the  root  acidity  of  100  plants  expressed  as 
citric  acid,  varies  from  0.34  per  cent,  with  Solanaceae  to  3.4  per 
cent,  with  Rosaceae,  and  averages  0.91  per  cent.  He  based  on 
this  work  a  method  of  estimating  the  available  plant  food  by 
extracting  the  soil  with  a  i  per  cent,  solution  of  citric  acid.  The 
method  was  applied  to  Rothamsted  soils.2  The  following  are 
some  of  the  results : 

BROADBAI.K  WHEAT  PLOTS. 


Treatment  of  50  years 

Dissolved  by  i  per  cent,  citric  acid 

Average 
yield, 
6  years, 
wheat 

Phos- 
phoric acid 

Pounds 
per  acre 

Potash 

Pounds 
per  acre 

Per  cent. 
0.0078 

0.0543 
0.0560 

2O2 

1418 
1307 

Per  cent. 
0.0032 

0.0232 
0.0384 

83 

602 
896 

bushels 
I2# 

33^ 
38^ 

7  Phosphoric  acid,  Potash, 

The  amount  of  phosphoric  acid  and  potash  dissolved  by  i  per 

1  Jour.  Chem.  Soc.,  1894,  115. 

*  Bulletin  106,  Office  Exp.  Sta.,  U.  S.  Dept.  Agr. 


ACTIVE   PLANT  FOOD,   ETC.  iSl 

cent,  citric  acid  thus  corresponds  with  the  treatment  of  the  plot 
and  the  yield  of  wheat.  The  phosphoric  acid  soluble  in  strong 
hydrochloric  acid  was  0.114  to  0.219  per  cent.,  potash  0.197  to 
0.285 ;  thus  while  there  was  some  difference,  it  is  not  a  clear 
indication  as  to  the  fertility  of  the  soil. 

The  application  of  the  citric  acid  method  to  soils  of  varying 
character  has  not  always  given  good  results.  This  may  be  due  to 
several  reasons :  ( i )  The  plant  may  have  greater  difficulty  in 
obtaining  citric  acid  soluble  plant  food  in  some  soils  than  in 
others.  In  other  words,  it  may  be  necessary  that  the  standard 
vary  according  to  the  character  of  the  soil,  as  Hilgard's  standards 
do.  (2)  The  soil  may  not  have  been  deficient  in  phosphoric  acid 
or  potash  when  it  was  supposed  to  be.  (3)  Different  rates  of 
change  of  potash  and  phosphoric  acid  into  more  soluble  com- 
pounds in  different  soils  may  interfere. 

According  to  Dyer,  less  than  o.oi  per  cent,  phosphoric  acid  or 
potash  soluble  in  phosphoric  acid  indicates  a  deficiency. 

Other  Weak  Solvents.1 — These  include  N/5  nitric  or  hydro- 
chloric acid,  N/2OO  hydrochloric  acid,2  and  N/5  oxalic  acid  which 
have  been  suggested  for  the  same  purpose  as  I  per  cent,  citric  acid. 
Some  of  these  solvents  have  the  advantage  of  greater  ease  of 
manipulation  than  citric  acid.  The  results  vary  according  to  the 
solvent  employed. 

The  most  promising  solvent  is  fifth-normal  nitric  acid.  Fifth- 
normal  nitric  or  hydrochloric  acid  gave  the  same  results  on  cer- 
tain of  the  Rothamsted  soils  as  citric  acid,  and  upon  some  other 
soils  tested  by  the  Association  of  Official  Agricultural  Chemists 
the  results  were  more  nearly  in  accordance  with  the  needs  of  the 
plant. 

Factors  of  Availability  of  Plant  Food.3 — The  amount  of  any 
given  plant  food  which  is  withdrawn  from  the  soil  by  the  plant 
does  not  depend  upon  one  condition  only,  but  is  dependent  upon 

1  See  Proceedings    Association  Official    Agr.  Chem.,  Bulletins  47,  49, 
51,  56,  67,  73,  Division  Chem.,  U.  S.  Dept.  Agr. 

2  Moore,  Jour.  Am.  Chem.  Soc.,  1912,  p.  791. 

3  Fraps,  Am.  Chem.  Jour.,  1904,  p.  i. 


l82  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

a    number    of    factors.     These    factors    may    be    grouped    as 
follows : 

(1)  The  quantity  of  the  element  present  at  the  beginning  of 
the  growing  season  in  forms  of  combination  which  can  be  partly 
or  completely  absorbed  by  the  plant.     This  may  be  called  chem- 
ically available  plant  food. 

(2)  The  condition  of  the  soil  particles.     Compounds  chem- 
ically available  may  be  enclosed  in  the  soil  particles  so  as  not  to 
be  exposed  to  the  action  of  plant  roots.     Such  compounds  are 
physically  unavailable.     If  the  encrusting  substance  is  removed, 
such  bodies  become  chemically  available. 

(3)  The  amount  of  the  plant  food  transformed  during  the 
growing  season  into  forms  of  combination  which  can  be  absorbed 
by  plants.     This  factor  is  certainly  of  importance  with  respect 
to  nitrogen;  its  importance  in  the  case  of  phosphoric  acid  and 
potash  is  apparently  not  so  great  but  the  matter  requires  study. 
This  factor  may  be  called  weathering  availability. 

(4)  The   nature   of   the   plant.      Plants   differ   in  both   their 
capacity  for  absorbing  food  and  their  need  of  it.     Whatever  the 
cause  of  these  differences,  there  is  no  doubt  but  that  they  exist. 
We  will  call  this  factor  physiological  availability. 

The  character  of  the  soil,  its  chemical  composition,  the  condi- 
tions which  prevail  during  the  growth  of  the  plant,  and  perhaps 
other  factors  influence  the  amount  of  plant  food  taken  up. 

Factors  Influencing  the  Composition  of  the  Soil  Extract.1 — The 
amount  of  phosphoric  acid  extracted  from  the  soil  by  a  given 
solvent  is  the  difference  between  that  dissolved  from  the  phos- 
phatic  or  potash  mineral  and  that  absorbed  by  the  fixing  particles 
of  the  soil.  That  is  to  say,  the  soil  extract  does  not  necessarily 
represent  the  solubility  of  the  mineral  exposed  to  the  action  of  the 
solvent,  but  is  the  resultant  of  the  solvent  and  fixative 
forces.  Furthermore,  the  quantity  of  phosphoric  acid  exposed 
to  the  action  of  the  solvent  depends  upon  its  con- 
dition in  the  soil  and  the  solubility  of  protecting  material  in  the 
solvent  used.  If  the  phosphate  mineral  is  enclosed  within  quartz, 
1  Texas  Bulletins  126-145. 


ACTIVE;  PLANT  FOOD,  ETC.  183 

it  is  quite  effectually  protected  from  any  solvent.  If  it  is  con- 
tained within  zeolites,  it  may  be  affected  by  some  solvents  and  not 
by  others.  If  it  is  contained  in  carbonate  of  lime,  the  latter  will 
be  dissolved  by  any  acid  solvents,  with  consequent  exposure  of  the 
included  phosphate  to  the  action  of  the  solvent. 

The  quantity  of  phosphoric  acid  or  potash  contained  in  the  soil 
extract  thus  depends  upon  three  factors : 

(1)  The  quantity  of  phosphate  or  potash  mineral  exposed  to 
the  solvent,  and  its  solubility  under  the  conditions  of  the  extrac- 
tion. 

(2)  The    solubility    of    the    soil    materials    which    protect   or 
enclose  phosphates  or  potash  compounds. 

(3)  The  power  of  the  soil  to  fix  phosphoric  acid  or  potash 
under  the  conditions  of  the  extraction. 

The  strength  of  the  solvent,  its  nature,  the  period  of  digestion, 
the  temperature,  and  the  proportion  of  soil  to  solvent,  all  affect 
the  quantity  of  phosphoric  acid  and  potash  contained  in  the  soil 
extract,  but  they  have  their  effect  through  action  on  the  three 
factors  mentioned  above. 

Solubility  of  the  Soil  Minerals. — This  subject1  is  studied  by 
bringing  phosphate  or  potash  minerals  in  contact  with  N/5  nitric 
acid,  in  the  proportions  in  which  these  minerals  may  occur  in  the 
soil,  and  under  the  conditions  of  the  soil  extraction. 

Phosphoric  Acid. — The  phosphates  of  lime  are  completely 
soluble,  the  precipitated  phosphates  of  iron  and  aluminium  are 
completely  soluble,  and  vivianite  and  triplite  are  nearly  so,  in  N/5 
nitric  acid.  The  aluminium  phosphates  (variscite  and  wavellite) 
and  the  basic  ferric  phosphates  are  comparatively  slightly  dis- 
solved. 

It  is  hardly  probable  that  ferrous  phosphate  (vivianite)  is  of 
common  occurrence  in  ordinary  cultivated  soils,  though  it  may 
exist  in  some  soils  which  are  not  well  aerated.  Fifth-normal 
nitric  acid  dissolves  calcium  phosphates  completely,  but  dissolves 
mineral  aluminium  phosphates  or  basic  ferric  phosphates  only  to 
a  slight  extent.  It  thus  distinguishes  between  these  two  classes 

1  Texas  Station  Bulletins  126-1.15. 


184  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

of  compounds  in  the  soil.  Apatite,  phosphate  rock,  ferric  phos- 
phate (precipitated),  aluminium  phosphate,  vivianite,  and  triplite 
are  practically  equally  soluble.  We  also  feel  justified  in  saying 
that  acid  phosphate  would  be  completely  dissolved.  But  no  one 
can  yet  claim  that  these  materials  possess  the  same  value  to  plants. 
Fifth-normal  nitric  acid  may  not  distinguish  between  minerals 
which  have  unequal  values  to  plants.  We  have  no  solvent  which 
would  dissolve  phosphoric  acid  from  the  phosphates  mentioned,  in 
the  same  proportions  as  would  be  taken  from  them  by  plants. 
What  we  cannot  do  with  known  mineral  phosphates  of  known 
character  outside  of  the  soil,  we  could  not  expect  to  do  with  the 
same  phosphates  after  they  are  put  into  the  soil,  and  with  the  un- 
known phosphates  already  within  the  soil. 

Soils  may,  therefore,  contain  equal  quantities  of  phosphoric 
acid  soluble  in  fifth-normal  nitric  acid,  and  yet  give  up  unequal 
quantities  of  phosphoric  acid  to  plants  on  account  of  differences 
in  the  phosphates  present.  This  consideration  must  give  rise  to 
caution  in  comparing  the  results  of  all  kinds  of  soils  with  one 
another. 

Only  those  soils  should  be  compared  which  probably  contain 
the  same  kinds  of  phosphates.  Soils  widely  dissimilar  in  origin 
and  character  should  not  be  compared,  unless  there  is  evidence 
that  they  contain  similar  phosphates. 

Study  of  potash  dissolved  from  minerals  in  a  similar  way  shows 
that  very  little  is  taken  from  the  felspars,  microcline  and 
orthoclase,  less  than  ten  per  cent,  from  glauconite  and  biotite,  and 
from  16  to  60  per  cent,  from  muscovite,  nephelite,  leucite, 
phillipsite,  and  apophyllite.  Potash  absorbed  by  chabazite  and 
some  other  minerals  is  extracted  to  the  extent  of  70  per  cent. 
The  dissolved  potash  thus  represents  a  large  portion  of  some 
easily  dissolved  mineral,  or  a  small  portion  of  some  difficultly 
attacked  mineral. 

Fixation  of  the  Dissolved  Phosphoric  Acid  and  Potash. — The  soil 
has  the  power  to  withdraw  potash  and  phosphoric  acid  from 
solution,  both  in  water  and  in  acids.  The  method  of  studying 
this  factor  consists  in  extracting  two  portions  of  the  soil  of 


ACTIVE   PLANT   FOOD,   ETC.  185 

known  fixing  power  with  the  solvent,  one  part  with  the  acid  alone, 
and  the  other  with  a  known  quantity  of  phosphoric  acid  or  potash. 
The  quantities  should  be  such  as  might  be  dissolved  from  the 
soil.  The  following  is  an  example  i1 

Phosphoric  acid 
Parts  per  million 

Extracted  from  soil  alone 8.5 

Added  to  solvent 194.0 


Total  present 202.5 

Actually  recovered 48.0 

Absorbed  by  soil 154-5 

With  17  soils,  the  fixation  of  the  added  phosphoric  acid  ranged 
from  5  to  94  per  cent,  of  the  quantity  added.  Thus  the  phos- 
phoric acid  extracted  by  the  N/5  nitric  acid  does  not  necessarily 
represent  that  which  has  gone  into  solution,  but  represents  the 
resultant  of  the  solvent,  and  the  fixing  power  of  the  soil.  With 
some  soils,  the  fixing  power  is  so  high  that  it  must  be  considered 
very  seriously  in  interpreting  the  results  of  the  analysis.  Fixation 
also  takes  place  from  acids  stronger  than  fifth-normal. 

Fixation  of  potash  takes  place  under  the  same  conditions  as  the 
fixation  of  phosphoric  acid,  but  to  a  much  less  extent,  and  the 
factor  of  fixation  is  much  less  important  with  potash. 

Soils  containing  easily-soluble  phosphoric  acid  or  potash  com- 
pounds give  decreasing  amounts  to  successive  extractions,  but 
soils  containing  little  or  no  compounds  of  high  solubility  give 
successive  extracts  of  nearly  constant  composition. 

Solubility  of  Constituents  of  the  Soil. — The  solubility  of  the 
constituents  of  the  soil  must  be  considered  as  a  factor  in  the 
analysis  of  soils  with  weak  solvents.  If  any  quantity  of  the  soil 
passes  into  solution,  phosphates  will  thereby  be  exposed  to  the 
action  of  the  solvent,  which  were  protected  from  the  action  of 
soil  moisture  and  roots,  and  which  are  really  physically  unavail- 
able. This  factor  must  be  given  careful  consideration.  For 
example,  N/5  nitric  acid  dissolves  320  parts  per  million  of  lime 
(CaO)  from  one  soil,  while  from  another  soil  it  dissolves  53,250 
parts,  which  corresponds  to  nearly  10  per  cent,  carbonate  of 
1  Texas  Station  Bulletin  126,  p.  16. 
13 


l86  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

lime.  The  amount  of  phosphoric  acid  and  potash  brought  into 
action  through  the  solution  of  the  lime  in  the  soil  first  named,  may 
not  be  large,  but  in  the  case  of  the  second  soil,  10  per  cent,  of  the 
soil  enters  into  solution,  and  all  the  phosphoric  acid  and  potash 
protected  within  this  10  per  cent,  is  exposed  to  the  action  of  the 
solvent.  This  action  is  further  emphasized,  in  the  case  of  the  soil 
just  mentioned,  by  the  fact  that  a  second  treatment  with  acid  dis- 
solves 43,400  parts  per  million  of  lime,  and  a  third  treatment  dis- 
solves 46,360  parts,  making  a  total  of  about  14  per  cent,  of  lime 
dissolved  from  the  soil,  corresponding  to  about  25  per  cent,  car- 
bonate of  lime. 

This  soil,  of  course,  represents  an  extreme  instance,  but  it 
emphasizes  the  difference  between  a  calcareous  and  a  non- 
calcareous  soil.  In  a  non-calcareous  soil,  the  phosphoric  acid  and 
potash  inclosed  within  the  soil  particles  are  protected  from  the 
solvent,  while  in  a  calcareous  soil,  that  portion  of  the  phosphates 
and  potash  minerals  included  in  the  calcareous  matter  dissolved 
by  the  acid  is  exposed,  and  may  be  dissolved. 

Since  the  plant  food  dissolved  from  a  non-calcareous  soil  is 
present  on  the  external  surface  of  the  soil  grains,  and  accessible 
to  the  roots  of  the  plants  and  the  action  of  soil  moisture,  while 
that  dissolved  from  calcareous  soils  is,  without  doubt,  in  part 
included  within  the  soil  grains,  and  not  accessible  to  plant  roots, 
it  is  obvious  that  calcareous  soils  may  contain  a  larger  quantity  of 
seemingly  active  plant  food  than  non-calcareous  soils,  and  yet 
require  fertilization  on  account  of  the  phosphoric  acid  being  pro- 
tected. 

Two  calcareous  soils  may  also  contain  the  same  amount  of 
active  plant  food,  and  yet  differ  in  the  amount  plants  can  take 
from  them.  In  one  the  plant  food  may  be  on  the  extreme  surface 
of  the  soil  grains,  in  the  other  it  may  be  disseminated  through 
them. 

Calcareous  soils  are  more  durable  than  non-calcareous  soils. 
This  may  be  explained  by  the  fact  that  the  gradual  weathering  of 
such  soils  continually  exposes  fresh  surfaces  of  plant  food. 


ACTIVE  PLANT  FOOD,   ETC.  187 

Significance  of  the  Dissolved  Plant  Food.1 — In  considering  the 
significance  of  the  dissolved  plant  food,  it  is  necessary  to  regard 
the  active  phosphoric  acid  and  potash,  the  "acid  consumed,"  and 
the  fixing  power  of  the  soil.  The  fixing  power  is  of  importance 
chiefly  in  connection  with  soils  which  fix  more  than  80  per  cent, 
phosphoric  acid.  With  such  soils,  the  extracted  phosphoric 
acid  may,  or  may  not,  represent  the  soluble  phosphates. 

The  "acid  consumed"  is  a  measure  of  the  bases  dissolved  by 
the  solvent,  and  is  estimated  by  titrating  10  cc.  of  the  solution 
after  the  extraction  is  complete. 

When  10  parts  per  million  of  phosphoric  acid,  or  less,  is 
extracted,  associated  with  a  fixing  power  of  less  than  50  per  cent., 
and  with  acid  consumed  less  than  90  per  cent.,  it  indicates  that 
practically  none  of  the  phosphoric  acid  of  the  soil  is  present  as 
apatite,  calcium  phosphate,  or  similar  compounds,  but  must  be 
present  as  basic  iron  or  aluminium  phosphates  or  in  organic  com- 
bination. When  10  parts  phosphoric  acid,  or  less,  are  present  and 
the  soil  has  a  high  fixing  power  for  phosphoric  acid  (75  per  cent, 
or  more),  calcium  phosphates  may  or  may  not  be  present.  That 
is  to  say,  the  method  can  not  in  this  case  distinguish  between 
phosphoric  acid  which  goes  into  solution  from  calcium  phosphate 
and  is  then  removed  by  fixation,  and  that  which  comes  from  the 
basic  phosphates  of  the  soil.  The  origin  of  the  soil  will  throw 
some  light  upon  the  matter.  If  the  soil  is  geologically  old,  the 
phosphoric  acid  has  probably  all  been  converted  into  basic  phos- 
phates. If  the  soil  has  been  recently  formed  from  rocks  contain- 
ing apatite  and  other  phosphatic  minerals,  it  is  possible  that  cal- 
cium phosphate  may  still  be  present  and  the  same  is  true  if  the 
soil  has  been  fertilized.  In  the  majority  of  soils  having  a  high 
fixing  power  and  a  low  content  of  phosphoric  acid,  provided  that 
.they  have  not  been  fertilized,  the  phosphoric  acid  is  probably 
present  as  basic  iron  and  aluminium  phosphates. 

A  soil  of  high  fixing  power  such  as  above  mentioned  would 
yield  up  the  same  quantity  of  phosphoric  acid  to  the  solvent, 
whether  fertilized  or  not  fertilized,  unless  a  very  heavy  applica- 
1  Texas  Station  Bulletins  126  and  145. 


1 88 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


tion  of  phosphoric  acid  has  been  made.  One  thousand  pounds  of 
16  per  cent,  acid  phosphate  would  represent  an  application  of  80 
parts  per  million  of  phosphoric  acid,  and  this  heavy  application 
would  not  increase  very  much  the  phosphoric  acid  removed  from 
soils  of  very  high  fixing  power. 

A  soil  containing  100  parts  per  million  of  phosphoric  acid,  with 
a  low  acid  consumed,  and  with  a  fixing  power  of  less  than  50, 
probably  contains  a  corresponding  amount  of  calcium  phosphate 
accessible  to  the  roots  of  plants. 


too 


30 


fiO 


40 


eo 


/        ?       3        4  5-6  7-3  3-10  1 1- IB 

GROUP.  BASED  ON  ACTIVE.  PHOSPHOR/C  ACID 

Fig-  39— Relation  of  the  active  phosphoric  acid  of  the  soil  to  the  phosphoric 

acid  withdrawn  by  crops  in  pot  experiments,  expressed 

as  bushels  corn  per  acre. 

A  soil  containing  100  parts  per  million  of  phosphoric  acid,  with 
an  acid  consumed  of  20  per  cent.,  may  or  may  not  expose  much 
phosphoric  acid  to  the  roots  of  plants.  It  is  impossible  to  say 
how  much  of  it  is  protected  by  the  calcareous  material. 

It  is  impossible  to  distinguish  phosphoric  acid  in  its  several 
different  forms.  For  example,  suppose  plots  were  fertilized 
with  equal  quantities  of  phosphoric  acid,  Thomas  phos- 
phate, phosphate  rock,  acid  phosphate,  and  apatite.  We 
could  not  expect  to  find  a  relation  between  the  phosphoric 


ACTIVE   PLANT  FOOD,   ETC. 


189 


acid  dissolved  from  these  plots  and  the  crop  production.  All 
these  materials  would  give  up  their  phosphoric  acid  equally  well 
to  the  solvent  used. 

A  soil  containing  less  than  50  parts  per  million  of  active  potash 
probably  contains  all  its  potash  in  the  form  of  highly  insoluble 
silicates,  such  as  the  felspars.  A  soil  containing  over  50  parts  per 
million  of  active  potash  contains  some  of  more  easily  dissolved 
potash  minerals  or  compounds.  Since  the  solvent  does  not 


Fig.  40. — Corn  grown  with  and  without  phosphoric  acid  on  four  soils  con- 
taining 60  to  100  parts  per  million  of  active  phosphoric  acid,  Te^as  Station. 

decompose  such  minerals  fully,  and  some  fixation  also  occurs,  the 
quantity  of  potash  extracted  is  less  than  the  quantity  present  in 
easily  soluble  compounds. 

Relation  of  Active  Phosphoric  Acid  to  Growth  in  Pot  Experi- 
ments.— At  the  Texas  Experiment  Station,  studies  were  made  of 
the  relation  between  the  active  phosphoric  acid  present  in  the  soil 
and  the  crop  produced  in  pot  experiments.  The  comparison  was 
made  between  the  crops  grown  with  phosphoric  acid,  nitrogen,  and 
potash,  and  those  grown  with  nitrogen  and  potash  only.  The 


190 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


behavior  of  the  corn  crop  was  closely  related  to  the  quantity  of 
active  phosphoric  acid  in  the  soil.  Soils  containing  20  parts  per 
million,  or  less,  of  active  phosphoric  acid  are  clearly  deficient  in 
phosphoric  acid.  Soils  containing  30  to  100  parts  per  million 


Fig.  41. — Corn  grown  with  and  without  phosphoric  acid  on  four  soils  con- 
taining less  than  ten  parts  per  million  of  active  phosphoric  acid,   Texas  Sta. 

were,  as  a  rule,  deficient.     Soils  containing  100  to  200  parts  per 
million  were  deficient  in  about  one-half  of  the  experiments. 
AVERAGE  CORN  POSSIBILITY  AND  AVAILABILITY  OF  PHOSPHORIC  ACID. 


Active  phosphoric  acid 


Corn  equivalent 
(bushels  per  acre) 


Average 

Maximum 

4r 

Q  O 

i*.0 

20  8 

31.0 

36  o 

iy-/ 

2/1     A 

o/-IJ 

A2  O 

60  to    80  

26  =; 

CQ    Q 

22  o 

^Q  O 

C2   C 

OV-^ 
IOI  O 

60  7 

QI  O 

The  quantity  of  phosphoric  acid  withdrawn  from  the  soil  was 
also  related  to  the  quantity  of  active  phosphoric  acid.     In  the 


ACTIVE  PLANT  FOOD,   ETC. 


191 


table1  on  page  190  the  quantity  of  phosphoric  acid  withdrawn  by 
the  crop  is  expressed  as  bushels  of  corn  per  acre  which  could  be 
produced  with  it. 

Potash? — A  similar  series  of  experiments  carried  out  with 
potash  lead  to  similar  results.  The  percentage  of  deficient  crops 
decreases  with  the  quantity  of  active  potash  in  the  soil.  The 
average  percentage  of  potash  in  the  crop  increases  with  the  per- 
centage of  active  potash  in  the  soil.  The  actual  quantity  of  potash 


POTASH  iu  SOIL  IN  PARTS  PER  MILLION 

Fig.  42. — Relation  of  the  potash  content  of  the  crop  to  the 
active  potash  of  the  soil. 

removed  by  the  crop  increases  with  the  active  potash  of  the  soil. 
After  cropping,  the  soil,  on  analysis,  was  found  to  contain  less 
active  potash  than  it  did  before  cropping,  showing  the  dis- 
appearance of  active  potash  due  to  the  crop. 

RELATION  OF  ACTIVE  POTASH  TO  POT  EXPERIMENTS. 


Active  potash  in  soil 

Percentag 

e  of  crops 

Average 
weight  of 
crops  without 

Average 
percentage 

(parts  per  million) 

Deficient 
in  potash 

Injured 
by  potash 

potash  divided 
by  crop  with 
potash 

of  potash  in 
corn  crop 

86  7 

6  7 

67 

T    l8 

cr    T 

16  7 

W 
7O 

I.JO 

IOO  to   I  SO  

OO'A 
CA     7 

16  i 

79 
SA 

l./U 
2   2Q 

^•Z9 

O7'1 

1  i  '•*• 

91 

•55 
i  &z 

O/'O 

61'6 

08 

3-°5 

^D-o 
Ac  6 

9° 

•53 

i  81 

l^.U 

18  o 

4o-u 
4"   8 

116 

3-°3 

4.5-° 

•31 

1  Texas  Station  Bulletin  126,  p.  69. 

2  Texas  Station  Bulletin  145. 


192 


PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 


The  actual  amount  of  potash  removed,  on  an  average,  from  the 
different  soils,  is  given  in  the  following  table.  In  order  to  make 
the  table  more  concrete,  the  amount  of  potash  is  also  expressed 
in  bushels  of  corn  per  acre  which  could  be  produced  by  this  quan- 
tity, both  stalk  and  grain  included : 


Active  potash  in  soil 
(parts  per  million) 

Active  potash  removed 
(parts  per  million) 

Corn  in 
bushels 
equivalent  to 
average  potash 
removed 

Average 

Maximum 

29.7 
37-2 

80^9 
I2O.O 

150.9 
II9.4 
^06.9 

53-4 
143-2 
176.2 
249.6 
434-6 
354-8 
295.8 
380.8 

58.6 

74-4 
102.0 
l6l.8 

240.2 
313.8 
238.8 
413.8 

CQ    to    IOO    •  • 

ioo  to  I  so  

Importance  of  the  Active  Plant  Food. — The  active  plant  food 
is  thus  related,  on  an  average,  to  the  ability  of  the  soil  to  supply 
plant  food.  Variations  undoubtedly  occur,  due  to  variations  in 
the  nature  of  the  active  plant  food.  The  relation  of  the  active 
plant  food  to  field  results  must  be  studied  and  worked  out. 
Deficiency  as  shown  in  pot  experiments  must  be  considered  as 
relative  deficiency,  and  in  applying  the  results  to  field  conditions, 
the  possibilities  of  the  soil  under  the  prevailing  climatic  condi- 
tions must  be  considered.  For  example,  in  our  pot  experiments, 
soils  containing  ioo  to  150  parts  per  million  of  active  potash  were 
deficient  in  potash  in  54.3  per  cent,  of  the  tests,  and  yet  on  an 
average,  they  gave  up  enough  potash  for  102  bushels  of  corn, 
the  maximum  being  352  bushels.  In  other  words,  the  pot  experi- 
ments demanded  more  potash  than  would  suffice  for  the  crop 
indicated  above.  Had  the  demands  for  potash  been  smaller,  the 
soil  would  not  have  been  deficient. 

The  importance  of  the  estimation  of  the  active  potash  and 
phosphoric  acid  is  to  show  the  relative  deficiency  of  the  soil  for 
these  elements.  The  tables  we  have  given  are  an  aid  in  this  con- 
sideration. For  example,  a  soil  containing  10  parts  per  million 
of  active  phosphoric  acid  and  50  parts  of  active  potash,  would 


ACTIVE   PLANT  FOOD,   ETC. 


193 


have  an  average  corn  possibility  of  4.5  bushels  for  phosphoric 
acid  and  58.6  bushels  for  potash.  Evidently  there  is  greater  need 
of  phosphoric  acid  than  of  potash,  and  the  two  become  equal  by 
the  addition  of  sufficient  phosphoric  acid  for  54.1  bushels  corn. 


/ 

7 

$ 

V 

S\ 

\/ 

7 

too 

^ 

/ 

80 

fy 

i 

f 

60 

J 

20 

**"* 

SO         /OO        I5O       2OO                        3OO                     4OO                       5OO                    6OO     S-T-* 

ACTIVE  POTASH  IN  Son.  //v  PARTS  PER  MILLION 

Fig.  43. — Relation  of  the  potash  removed  by  crops  in  pot  experi- 
ments to  the  active  potash  contained  in  the  soil. 

This,  however,  is  only  an  illustration.     Field  experiments  must 
show  the  exact  relation  of  the  two. 

Relation  of  Total  Nitrogen  to  Results  of  Pot  Experiments.1 — Pot 
experiments  similar  to  these  just  described  have  been  used  to 
trace  the  relation  between  the  total  nitrogen  of  the  soil  and  the 
effect  of  the  fertilizers.  They  will  be  described  here  on  account 
of  their  relation  to  the  preceding  work.  The  effect  of  the  fertilizer 
is,  in  general,  related  to  the  content  of  nitrogen  in  the  soil.  The 
percentage  of  nitrogen  in  the  crop  increases  as  the  percentage  of 
total  nitrogen  of  the  soil  increases.  The  average  corn  possibility, 
1  Texas  Station  Bulletin  No.  151. 


194  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

in  bushels  per  acre,  based  on  the  quantity  of  nitrogen  removed 


/9 
If 

/ 

/ 

5a/2 

/\ 

/ 

4'* 

A/^ 

•^X 

X"- 

-S 

^V 

A 

1 

fQ 

A 

/ 

"T 
/ 

/ 

j 

JO+        Of       .OB        .10         .11 


.16      ./a     .&     21 


Fig.  44. — Relation  of  total  nitrogen  to  the  average  weight  of  the  crops 
grown  without  addition  of  nitrogen  in  pot  experiments. 


500 


\       I 

os  wif/touf-  Ntfrogefi 


PERCENTA  GE5  OF  NITROGEN  IN  SOIL 

Fig.  45.— Relation  of  total  nitrogen  of  the  soil  to  the  average  effect 
of  fertilizer  nitrogen  in  pot  experiments. 


from  the  soils  in  pot  experiments,  is  given  in  the  following  table 


ACTIVE  PLANT  FOOD,  ETC. 


Average 
sibil 


Percentage  of  corn  possibility 

nitrogen  in  soil  (bushels  per  acre) 

O.OOO  to  O.O2    5-7 

O.O2I  to  0.04 9.4 

0.041  to  0.06  13.6 

0.061  to  o.  16 22.3 

o.i6itoo.i8 42.9 

Interpretation  of  Soil  Analysis  with  Weak  Solvents. — The  "corn 
possibility"  figures  may  be  used  for  the  purpose  of  ascertaining 
the  probable  relative  deficiency  of  a  soil.  Suppose,  for  example, 
a  soil  contains  .086  per  cent,  nitrogen,  8  parts  per  million  active 
phosphoric  acid,  and  105  parts  per  million  active  potash. 
Referring  to  the  tables,  we  find : 

Corn  possibility 
(bushels) 

For  nitrogen 22.0 

For  active  phosphoric  acid 4.5 

For  active  potash 102.0 

Thus  this  soil  would  probably  be  most  deficient  in  phosphoric 
acid,  next  in  nitrogen,  and  least  in  potash,  if  tested  in  pot  experi- 
ments. 

The  active  phosphoric  acid  and  potash  and  the  total  nitrogen 
are  not,  however,  the  only  things  to  consider  under  field  con- 
ditions. The  form  of  the  phosphoric  acid,  depth  of  soil,  kind  of 
cultivation,  season,  etc.,  all  influence  the  size  of  the  crop.  It  is 
thus  not  possible  to  say  that  the  corn  possibility  represents  what 
should  actually  be  produced  in  the  field.  Field  results  must  be 
worked  out  for  different  localities,  as  no  doubt  climate  and  tem- 
perature will  cause  soils  of  the  same  analysis  to  give  different 
results  in  different  sections. 

The  fact  that  there  is  possibly  a  close  relation  between  chemical 
analyses  and  field  results  is  shown  in  certain  results  secured  at 
the  Texas  Experiment  Station.1  Eight  soils  in  which  total 
nitrogen  was  probably  the  controlling  condition,  averaged  n 
bushels  per  acre  corn  possibility,  while  the  actual  yield  as  claimed 
by  the  farmers  was  18  bushels.  Five  soils  controlled  by  active 
1  Proc.  Int.  Cong,  of  Applied  Chem.,  1912. 


196 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


phosphoric  acid  averaged  12  bushels  corn  possibility,  and  actual 
production  averaged  14.  Considering  the  fact  that  the,  actual 
yields  given  were  estimates,  and  that  the  corn  possibility  is  prob- 
ably a  little  low,  the  agreement  is  good.  This  matter  requires  con- 
siderably further  study. 

Water-Soluble  Constituents. — The  water-soluble  constituents  of 
the  soil  are  of  significance  from  the  fact  that  material  can  enter 
the  plant  only  in  solution.  The  root  is  composed  of  cells, 
through  which  there  are  no  openings  for  the  entrance  of  solids. 

\Yhen     a     liquid     containing     a     substance     in     solution     is 


Fig.  46.— Enlarged  plant  cell,  normal  below,  and  with  the  protoplasm 
contracted  by  nitrate  of  soda  above. 

brought  in  contact  with  another  portion  of  the  same 
liquid  which  does  not  contain  that  substance,  the  dissolved  sub- 
stance passes  into  that  portion  until  all  parts  of  the  liquid  have  a 
uniform  composition.  This  is  called  diffusion.  The  same  occurs 
when  the  liquid  is  separated  by  a  membrane,  which  the  dissolved 
substance  is  able  to  penetrate.  Substances  which  cannot  generally 
pass  through  membranes  are  termed  colloids,  examples  being 
albumen,  glue,  etc.  Salt,  sugar,  calcium  sulphate,  which  can  pass 
through,  are  called  crystalloids.  If,  then,  a  plant  cell  is  brought 


ACTIVE:  PLANT  FOOD,  ETC.  197 

in  contact  with  a  solution  of  a  substance  which  can  penetrate  the 
membrane,  diffusion  will  take  place  until  the  number  of  ions 
of  the  same  kind  entering  the  cell  walls  is  equal  to  the  num- 
ber leaving  it.  If  the  cell  life  appropriates  any  of  the  ions,  and 
holds  them,  so  that  they  become  incapable  of  diffusion,  the  ions 
continue  to  enter  the  cell  until  the  cell  life  becomes  satisfied,  and 
the  number  entering  and  leaving  become  equal.  The  same 
phenomenon  occurs  with  an  aggregate  of  cells  or  the  entire  plant. 
It  is  then  possible  for  plants  to  extract  elements  from  very  dilute 
solutions,  and  accumulate  them  in  their  tissues,  and  also  for  plants 
to  live  in  comparatively  strong  solutions  of  a  salt  without  taking 
up  large  quantities  of  the  substance. 

Diffusion  into  Cells. — According  to  Pfeffer,  plant  cells  are 
composed  of  three  parts ;  an  outer  cell  wall,  of  cellulose  or  some 
other  membrane ;  a  layer  of  protoplasm  or  living  material  adherent 
to  the  cell  wall ;  and  the  cell  sap.  The  cell  wall  is  in  general  more 
permeable  to  dissolved  substances  than  the  protoplasm,  and  hence 
many  substances  pass  through  the  cell  walls  but  not  through  the 
living  plasma  within.  "It  is  indeed  possible  that  the  water  and 
salts  absorbed  by  the  roots  pass  mainly  if  not  entirely  through  the 
walls  of  living  cells  or  the  walls  and  cavities  of  dead  wood  fibers, 
so  that  only  on  reaching  the  leaves  of  a  tree  do  they  penetrate  the 
living  protoplasts  there."  The  character  of  the  cell  wall  and  of 
the  protoplasm  membranes  determine  whether  a  given  substance 
will  penetrate  to  the  interior  of  a  cell,  and  any  such  substance 
will  continue  to  be  absorbed  until  a  condition  of  equilibrium  is 
reached,  when  all  further  absorption  ceases.  If  this  condition  of 
equilibrium  is  disturbed,  absorption  may  continue,  and  relatively 
large  quantities  of  a  particular  substance  may  be  absorbed  from 
a  very  dilute  solution. 

Every  substance  which  can  pass  through  the  different  cellular 
membranes  penetrates  the  protoplasm  independently  of  whether  it 
is  useful,  unnecessary,  or  even  injurious. 

Cells  may  convert  bodies  which  diffuse  into  them  into  non- 
diffusing  compounds,  and  the  substance  will  continue  to  enter  as 
long  as  this  takes  place.  The  non-diffusing  compound  may  be 


198  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

soluble  or  insoluble.  Thus  methyl  blue  is  fixed  in  an  insoluble 
form  in  the  roots  of  Azalla,  while  in  the  roots  of  Lemna  minor  it 
accumulates  in  a  dissolved  form.  In  both  cases  the  dye  is 
accumulated  from  very  dilute  solution,  and  the  cells  become  dis- 
tinctly colored.  The  dissolved  substances  in  the  cell  sap  (sugar, 
salts  of  organic  acids,  potassium  nitrate,  etc.,)  must  be  present  in 
a  non-diffusing  form.  The  presence  of  nitrates  in  dead  cells 
does  not  indicate  that  they  are  so  present  in  the  living  cell,  for  the 
non-diffusing  substances  may  decompose  immediately  on  the 
death  of  the  cell. 

Transpiration  Movements. — Diffusion  alone  is  a  very  slow 
movement.  It  requires  319  days  to  transport  I  mg.  the  distance 
of  i  mm.  from  a  10  per  cent,  solution  into  pure  water.  Most  of 
the  material  which  enters  the  roots  of  a  plant,  though  it  must 
diffuse  through  the  root  wall,  enters  in  the  current  of  water  after- 
wards transpired,  rather  than  by  diffusion  alone. 

Active  transpiration  must  lead  to  the  continuous  introduction 
of  new  traces  of  salts  by  the  water  current,  since  backward 
diffusion  is  slow.  This  explains  how  relatively  large  amounts  of 
saline  materials  are  sometimes  found  in  plants.  Nobbe  and 
Siegert  actually  found  patches  of  saline  incrustation  on  the  leaves 
of  buckwheat  and  barley  when  the  plants  were  grown  in  a  one 
per  cent,  solution  of  salts.  Soluble  incrustations  are  sometimes 
found  on  plants,  and  calcareous  scales  are  often  found  on  the 
leaves  of  many  Saxifrage  and  other  plants.  Transpiration  may 
also  aid  in  the  deposition  of  silica  in  the  cells  of  plants. 

Absorption  by  the  Root. — Excepting  carbon  dioxide  (and  nitro- 
gen in  some  cases  perhaps)  the  roots  absorb  all  the  compounds 
used  to  buld  up  the  plant ;  namely,  water,  hydrogen,  and  oxygen, 
and  all  the  other  elements  in  the  form  of  salts.  Salts  of  iron,  cal- 
cium, magnesium,  sodium,  manganese,  potassium,  silicon,  chlorine, 
nitrogen,  sulphur,  and  phosphorus  are  thus  taken  up. 

Salts  in  solution  are  more  or  less  decomposed  into  ions,  which 
are  atoms  or  groups  of  atoms  charged  with  electricity.  Thus, 
sodium  chloride  is  broken  down  into  the  ions,  Na  and  Cl,  sodium 
sulphate  into  Na  and  SO4,  potassium  nitrate  into  K  and  NO3. 


ACTIVE:  pivANT  FOOD,  ETC.  199 

Plants  have  the  capacity  of  taking  up  one  or  the  other  of  these 
ions  alone.  From  a  solution  of  potassium  chloride,  the  plant  may 
take  up  more  potassium  ions  than  chlorine  ions,  leaving  hydrogen 
in  place  of  the  potassium.  The  liquid  would  then  become  acid 
from  the  presence  of  hydrochloric  acid.  The  plant  may  remove 
the  nitrate  ions  from  a  solution  of  calcium  nitrate.  The  calcium 
ion  would  then  unite  with  carbon  dioxide  and  form  insoluble  cal- 
cium carbonate. 

The  above  considerations  are  essentially  modified  in  the  pres- 
ence of  two  or  more  salts ;  as  a  rule,  when  two  salts  are  present, 
which  are  required  by  the  plant,  their  absorption  is  accelerated. 
For  example,  potassium  salts  are  taken  up  in  much  larger  quantity 
when  a  calcium  salt  is  present.  Potassium  nitrate  may  be  entirely 
removed  from  a  solution  containing  calcium  nitrate.  In  the 
presence  of  other  ions,  the  potassium  ion,  nitrate  ion,  phosphate 
ion,  and  sulphate  ion  can  be  completely  removed  from  solution, 
while  calcium  or  magnesium  ions  become  more  concentrated  in 
the  solution,  as  a  rule. 

A  study  of  the  effect  of  the  amount  of  water  evaporated  upon 
the  ash  constituents  taken  up  has  shown  that  the  stronger  the 
evaporation,  the  more  dilute  is  the  solution  taken  up  by  the  plant, 
but  at  the  same  time  the  more  substance  is  taken  up,  since  the 
decrease  in  concentration  is  in  a  less  ratio  than  the  increase  in 
water  evaporated. 

Soil  Solution. — The  soil  solutions  are  exceedingly  dilute.  From 
what  has  been  said,  however,  it  is  seen  that  plants  may  withdraw 
nourishment  from  very  dilute  solutions.  It  is  self-evident,  that 
when  the  dilution  goes  below  certain  limits,  diffusion  will  not 
take  place  with  sufficient  rapidity  to  satisfy  the  requirements  of 
the  plants,  and  limits  are  conceivable  at  which  only  a  minimum 
growth  w^ill  take  place. 

In  other  words,  there  is  an  optimum  of  concentration,  above 
and  below  which  a  lesser  production  of  plant  substance  takes 
place.  Below,  because  transpiration  and  diffusion  do  not  provide 
sufficient  food. 


2OO 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


An  example  of  the  effect  of  dilution  is  presented  below. 

Yields  gm.  dry  matter 

i  part  per  thousand  0-4934 

3  parts  per  thousand  0.7320 

5  parts  per  thousand  i .  1540 

The  plants  were  grown  in  water  containing  a  mixture  of  the 
various  necessary  salts. 

Solvent  Action  of  Roots. — Although  plants  can  take  up  sub- 
stances only  in  a  state  of  solution,  they  have  some  power  of 
bringing  substances  into  solution.  Etchings  showing  the  shape 
of  the  root  can  be  obtained  by  causing  plants  to  grow  upon 
polished  marble,  and  such  etchings  are  often  found  in  nature. 

The  solvent  action  of  roots  is  aided  by  the  intimate  contact 
between  root  hairs,  and  soil  particles,  the  latter  often  being 
literally  imbedded  in  the  roots.  The  solvent  action  observed  may 
be  brought  about  by  the  action  of  carbonic  acid  given  off  by  the 
roots,  and  the  etchings  mentioned  above  may  be  formed  in  this 


Fig.  47.— A  root  hair,  highly  enlarged,  showing  the  intimate 
contact  of  root  and  soil. 

manner.  According  to  Czapek,  roots  excrete  potassium  acid 
phosphate,  which  has  an  acid  reaction.  The  vegetable  acids  in 
the  root  juices  may  also  be  effective,  without  actually  passing 
through  the  membrane.  The  vegetable  acids  are  dissociated  to  a 
certain  extent  into  hydrogen  and  other  ions ;  for  example,  oxalic 
acid  may  dissociate  into  the  ions  H  and  HC2O4.  The  ion  HC2O4 
may  be  held  in  a  non-diffusing  condition,  while  the  hydrogen  is  at 
liberty  to  pass  through  the  membrane,  and  thus  exert  an  action 
upon  external  substances.  In  this  way  there  may  be  an  exchange 
of  H  and  Ca  ions,  for  example.  Whatever  the  cause  of  the 
solvent  action  of  plant  roots,  it  is  well  demonstrated  that  plants 
can  take  up  material  not  dissolved  in  the  solution  which  extends 
between  the  soil  particles. 


ACTIVE  PLANT  FOOD,   ETC. 


2O I 


Water  Extract  of  Soils. — In  arid  climates,  water-soluble  mate- 
rial may  accumulate  and  give  rise  to  alkali.  The  solvent  action 
of  water  in  a  soil  under  natural  conditions  is  increased  by  the 
carbon  dioxide  formed  from  decaying  organic  material. 

On  shaking  a  soil  with  water,  a  small  amount  of  soil  ingredients 
enters  into  solution.  The  extract  does  not  represent  the  solubility 
of  the  soil  constituents  in  water,  but  is  the  resultant  of  the  solvent 
and  fixative  forces,  as  in  the  case  of  the  acid  extract.  The  soil 
has  a  much  greater  power  of  withdrawing  material  from  water 
than  from  acid  solution,  and  hence  the  aqueous  extract  is  a  much 
poorer  measure  of  the  solubility  of  soil  materials.  For  example,1 
on  shaking  a  certain  soil  with  water,  the  resulting  extract  con- 
tained 2.3  parts  per  million  of  phosphoric  acid,  and  the  same 
results  were  secured  on  shaking  it  with  a  solution  of  potassium 
phosphate  containing  10  parts  per  million  of  phosphoric  acid. 

Composition  of  the  Water  Extract. — The  soil  extract  varies 
widely  in  composition,  even  from  soils  of  the  same  type.  The 
following  results  are  compiled  (and  recalculated)  from  Bulletin  22 
of  the  Bureau  of  Soils : 

VARIATIONS  IN  COMPOSITION  OF  SOIL  EXTRACT. 


Parts  per  million  of  soil 

Pounds  per  acre-foot 

Phosphoric 
acid 

Nitrogen 

Potash 

Phosphoric 
acid 

Nitrogen 

Potash 

Windsor  sand  . 
Norfolk  sand  •  . 
Sassafras  loam  . 
Leonard  town 
loam  

1.6-  7.6 
1.0-  9.7 
1.3-12.7 

1.7-  9.7 
1.4-24.0 

N 

0.2-    7.2 
0.2-    6.4 
O.I-IO.4 

trace  16.5 

trace    7.7 
trace    9.2 

K.2O 

13-1-  55-3 
13.9-  54.0 
9-5-  56.2 

72.1-  62.0 

9.0-  87.2 
5.9-100.6 

5.6-26.6 
3.5-53.9 
4-5-44-5 

1.0-57.1 
14.9-88.0 

N 

0.7-25.2 
0.7-22.4 
0.3-36.4 

trace  57.8 

trace  26.9 
trace  32-2 

K2O 

45.8-193.6 
48.7-189.0 

42.3-217.0 

31.5-285.2 
20.7-352.1 

Cecil   sandy 

Cecil  clay  

The  Bureau  of  Soils  claims  that  the  composition  of  the  soil 
extract  is  practically  constant  in  all  soils,  but  it  is  difficult  to  see 
how  the  preceding  analyses  can  be  reconciled  with  such  claim. 
1  Texas  Station  Bulletin  82,  p.  16. 


2O2 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


If  we  assume  that  in  the  production  of  one  gram  of  dry  matter 
500  grams  water  are  transpired,  we  can  calculate  the  concentration 
of  the  absorbed  water  required  to  give  the  average  composition  of 
various  plants.  This  has  been  done  and  the  results  are  in  the 
following  table : 


Percentage  in 
dry  matter  of  plant 

Necessary  concentration  of 
soil  solution  per  million 

Phosphoric 
acid 

Potash 

Phosphoric 
acid 

Potash 

o-59 
0.80 

o.'68 
0.67 
0.16 
0.66 
0.63 

1.86 
2.36 
1.94 
2.62 
1.65 
0.45 
2.22 

1-73 

IO 
16 
II 
14 
13 
3 
13 
13 

37 
47 
39 
52 
33 
9 
44 
15 

Winter  wheat  (bloom). 

Red.  clover  

Alfalfa 

If  we  compare  this  table  with  the  preceding,  we  find  that  the 
soil  moisture  does  not  contain  enough  phosphoric  acid.  In  only 
three  of  the  soil  series  is  even  the  maximum  content  of  phos- 
phoric acid  sufficient  for  the  requirements  of  any  of  the  plants 
(except  sugar  cane).  The  minimum  content  of  the  soil  moisture 
in  potash  falls  below  the  concentration  required,  but  the  maximum 
of  all  series  of  soils  is  above  the  maximum  requirements  of  the 
plants  given  above. 

Investigations  were  made  by  King1  upon  the  water-soluble  salts 
of  the  soil,  and  the  yield  of  corn  and  potatoes  on  eight  types  of 
soil  in  North  Carolina,  Maryland,  Pennsylvania,  and  Wisconsin. 
He  concludes  that  "there  is  a  well-marked  tendency  for  larger 
amounts  of  water-soluble  salts  to  be  removed  by  the  methods 
adopted  from  the  soils  upon  which  the  crops  have  made  the 
largest  yields."  The  water-soluble  material  was  estimated  to  the 
depth  of  four  feet.  The  addition  of  fertilizers  was  also  found  to 
increase  the  water-soluble  salts,  and  where  determined  under  large 
and  under  small  plants  in  the  same  field,  differences  were  also 
1  Bulletin  26,  Bureau  of  Soils. 


ACTIVE  PLANT  FOOD,  ETC. 


203 


evident,  as  the  soil  under  the  larger  plants  contained  more  water- 
soluble  materials. 

The  following  table  shows  the  water-soluble  material  dissolved 
from  several  types,  according  to  King's1  investigations : 

SAI/TS  DISSOLVED  BY  WATER  FROM  SURFACE  FOUR  FEET  OF  SOIL 
TYPES  (POUNDS  PER  ACRE). 


K 

Ca 

Mg 

N03 

HPO4 

Norfolk  sandy  soil    

210 

I92 
246 

257 

404 
415 
387 

1,036 
910 
1,070 
1,049 

177 
306 

420 

162 

147 
128 
262 
429 

200 

120 
221 

196 

Selma  silt  loam  

Norfolk  sand  

Sassafras  sandy  loam  

Hagerstown  clay  loam  .... 

224 

705 

,63 

1  06 

66 

The  average  quantity  of  plant  food  dissolved  from  the  soil  was 
sufficient  to  produce  the  following  amounts  of  clover  hay:2 

Tons 

Potash   7.2 

Lime 24.6 

Nitrogen 2.7 

Phosphoric  acid 13.2 

1  Bulletin  26,  p.  65,  Bureau  of  Soils. 

2  Bulletin  20,  p.  78,  Bureau  of  Soils. 


CHAPTER  XL 


CHEMICAL  CHANGES. 

The  soil  is  not  inert,  but  a  great  number  of  changes  take  place 
in  it.  some  purely  chemical,  and  others  brought  about  by  the 
action  of  bacteria  and  other  forms  of  life.  The  most  important 
changes  have  to  do  with  organic  matter  and  nitrogen.  The  bulk 
of  the  nitrogen  in  organic  forms  in  soils  is  useless  to  plants,  and 
must  be  changed  before  it  can  be  taken  up  by  them.  Phosphoric 
acid  and  potash  are  fixed  by  the  soil,  and  their  compounds  under- 
go various  changes. 

Changes  of  Nitrogen  in  the  Soil. — Many  changes  take  place  in 
the  nitrogen  of  the  soil,  all  brought  about  by  bacteria.  There  is, 
first,  the  transformation  of  organic  nitrogen  into  ammonia, 
termed  ammonification.  Next  is  the  change  of  organic  matter, 
ammonia,  and  nitrites,  to  nitrates,  a  change  called  nitrification. 
Another  change  is 'the  destruction  of  nitrates,  either  nitrites, 
ammonia,  protein,  or  free  nitrogen  being  formed,  a  change  called 
dentrification.  A  further  change  is  the  production  of  organic 
compounds  from  the  elementary  nitrogen  of  the  air,  a  change 
caled  nitrogen  fixation.  As  these  changes  are  brought  about  by 
the  agency  of  bacteria,  it  is  necessary  to  give  a  little  space  to  the 
study  of  soil  bacteria. 

Soil  Bacteria.1 — Bacteria  are  organisms  so  small  as  to  be  seen 
only  under  the  highest  power  of  the  microscope.  They  are 
grown  either  in  liquids  or  on  the  surface  of  slices  of  potatoes, 
solidified  plates  of  gelatin,  agar,  or  similar  material,  the  proper 
nourishment  being  supplied.  The  plate  method  is  used  for  isolat- 
ing and  studying  bacteria,  since  many  kinds  of  bacteria  form 
characteristic  colonies,  and  a  pure  culture  can  easily  be  secured 
therefrom.  Unfortunately  many  important  soil  bacteria  do  not 
grow  well  on  such  plates.  This  is  especially  true  of  the  nitrate 
bacteria.  Since  bacteria  abound  everywhere,  it  is  necessary 
in  the  study  of  bacteria  to  destroy  all  those  which  are  originally 

1  Review  of  Investigations  of  Soil  Bacteriology,  Voorhees  and  Lipman, 
Bulletin  94,  Office  of  Kxp.  Sta. 


CHEMICAL    CHANGES 


205 


present  in  the  vessels  or  materials  which  are  to  contain  those  to 
be  studied,  and  to  guard  as  much  as  possible  against  contamina- 
tion from  outside  sources,  such  as  the  air.  Bacteria  may  be  pres- 


Fig.  48.— Colonies  of  bacteria  growing  in  a  gelatine  plate.  Kansas  Station. 

ent  as  spores  which  are  a  resting,  or  "seed"  stage  of  bacteria,  and 
are  much  more  difficult  to  destroy  than  the  growing  bacteria. 

Methods. — Forceps,  cover  slides,  etc.,  are  sterilized  by  heating 
in  a  bunsen  burner.  Glassware,  such  as  flasks,  beakers,  pipettes, 
etc.,  and  other  articles  which  can  be  subjected  to  it,  may  be 
sterilized  by  dry  heat  one  hour  in  an  air  bath  or  oven  at  a  tem- 
perature of  170°  C.  In  order  to  prevent  contamination  after 
sterilization,  they  are  placed  in  closed  vessels  until  needed.  Flasks 
and  pipettes  may  be  plugged  with  cotton  wool,  which  allows  the 
entrance  of  air,  but  excludes  bacteria. 


2O6  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Distilled  or  tap  water  is  sterilized  by  boiling.  Boiling  for  five 
minutes  will  kill  ordinary  germs  if  no  spores  are  present.  Media 
are  often  sterilized  by  heating  in  steam  at  100°  C.  Steaming  one 
and  one-half  hours  will  sterilize  any  medium,  but  this  injures 
some  media,  especially  gelatin.  The  method  adopted  in  such 
cases  is  to  steam  for  15  minutes  on  three  successive  days.  This 
rests  on  the  principle  that  all  bacteria  in  the  non-spored  condition 
are  killed  the  first  day,  while  the  spores  which  are  not  killed, 
develop  into  bacteria  and  are  killed  the  second  or  third  day.  A 
rapid  and  effective  method  of  sterilization  consists  of  steaming 
under  pressure  at  115°  C.  from  7  to  15  minutes. 

A  variety  of  media  are  used  for  growing  bacteria,  such  as  meat 
extract,  broth,  blood  serum,  milk,  slices  of  potatoes,  etc. 

Number  of  Bacteria. — One  method  of  estimating  the  number 
of  bacteria  in  the  soil  is  as  follows :  About  a  gram  of  the  soil  is 
shaken  from  a  weighed  tube  into  a  liter  of  sterilized  water,  and 
the  tube  reweighed.  The  soil  and  water  are  then  mixed  thor- 
oughly. Tubes  of  modified  agar1  are  then  melted,  and  one  inocu- 
lated with  o.i  cc.  of  water,  another  with  i.o  cc.  The  agar  is  then 
poured  into  flat  dishes  provided  with  a  cover  (petri  dish)  which 
have  previously  been  sterilized,  and,  after  the  gelatin  has 
hardened,  it  is  set  aside  for  the  colonies  to  develop.  This  pro- 
cedure is  termed  plating.  Each  kind  of  bacterium  that  will  grow 
upon  the  material  used,  produces  a  characteristic  group  or  colony. 

The  colonies  are  then  counted.  For  example,  if  i  cc.  of  water 
is  used  and  100  bacteria  developed,  the  soil  contains  100,000  to  the 
gram,  since  the  quantity  of  water  used  was  shaken  with  o.ooi 
gram  soil. 

The  number  of  bacteria  counted  in  this  way  in  the  soil  is  some- 
what variable ;  from  8,000  to  6,000,000  per  cubic  centimeter  have 
been  found  in  the  surface  soil.  The  number  decreases  with  the 
depth,  until  at  the  5th  to  6th  foot  comparatively  few  are  found. 
The  following  is  an  example  of  such  a  test : 

1  P.  E.  Brown,  Iowa  Research  Bulletin  No.  2. 


CHEMICAL   CHANGES  2O/ 

Number  of  bacteria 
Inches  in  one  gram  soil1 

2 1 ,330,000 

4 1,500,000 

6 1,900,000 

8 260,000 

10 265,000 

12 124,000 

The  number  of  bacteria  so  counted  appears  to  have  no  direct 
relation  to  the  ammonifying,  nitrifying,  or  denitrifying  power  of 
the  soil.  Important  groups  of  soil  bacteria,  such  as  the  nitrify- 
ing, do  not  develop  colonies  at  all.  The  bacterial  count  appears 
to  be  more  closely  related  to  the  organic  matter  content  than  to 
anything  else.  If  it  is  desired  to  study  the  bacteria  further,  the 
desired  medium  is  inoculated  with  a  portion  of  a  colony  grown  on 
the  plate. 

Another  method-  of  estimating  the  number  of  bacteria  consists 
in  inoculating  a  series  of  suitable  media  from  different  dilutions 
of  the  soil,  say  equal  to  i  mg.,  o.i  mg.,  .01  mg.,  and  .001  mg.  of 
soil.  Suppose  that  with  ten  tubes  inoculated  from  .01  mg.  soil, 
7  nitrify  and  3  do  not.  Then  we  estimate  that  7  bacteria  were 
present  in  10  times  .01  mg.  soil,  or  7,000  are  present  in  a  gram. 
The  solution  for  inoculating  is  prepared  by  shaking  the  soil  with 
sterilized  water  as  described  above. 

Kinds  of  Soil  Bacteria.3 — The  general  tendency  of  bacterial 
action  in  the  soil  is  along  well  denned  lines,  although  reverse 
changes  occur  and  complicate  the  process.  Organic  matter,  by 
decay  or  putrefaction,  is  finally  converted  into  carbon  dioxide, 
water,  ammonia  or  nitrates,  and  mineral  salts.  Some  soil  bacteria 
produce  organic  matter  from  hydrogen  or  marsh  gas  and  carbon 
dioxide,  or  use  other  inorganic  materials  (sulphur,  or  sulphides) 
as  a  source  of  energy,  but,  in  spite  of  this,  the  general  movement 
is  as  indicated.  The  general  movement  of  organic  nitrogen  is 
towards  the  form  of  nitrates,  through  ammonia,  in  spite  of  the 
presence  of  bacteria  which  act  in  the  reverse  direction  and  con- 

1  Chester,  Delaware  Bulletin  No.  65. 

-  Wiley,  Principles  and  Practice,  Agr.  Chem.  Anal.,  Vol.  i. 

3  Kansas  Bulletin  117  ;  New  Jersey  Bulletin  40. 


2C>8  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

vert  nitrates  into  ammonia  or  bacterial  substances,  or  ammonia 
into  bacterial  substance.  Under  special  conditions  favorable  to 
the  growth  of  the  bacteria  concerned,  these  reverse  tendencies 
may  predominate,  or  develop  to  such  an  extent  as  to  materially 
modify  the  final  results. 

The  bacteria  which  affect  the  soil  nitrogen  are  very  important. 
Stoklosa1  divides  the  bacteria  into  seven  groups  with  respect  to 
their  action  towards  nitrogen : 

1 i )  Bacteria  which  decompose  nitrogenous  organic  bodies  and 
produce  ammonia. 

(2)  Bacteria  which  oxidize  ammonia  to  nitrites. 

(3)  Bacteria  which  oxidize  nitrites  to  nitrates. 

(4)  Bacteria  which  reduce  nitrates  to  nitritec  and  ammonia. 

(5)  Bacteria  which  reduce  nitrates  to  nitrites  and  the  latter  to 
elementary  nitrogen. 

(6)  Bacteria  which  change  ammonia,  nitrites  or  nitrates  into 
protein  or  bacterial  body  substance.     This  includes  members  of 
all  the  other  groups. 

(7)  Bacteria  which   fix   atmospheric   nitrogen   and   use   it  to 
form  compounds. 

Bacteria  have  been  found  in  the  soil  which  take  oxygen  from 
sulphates,  thus  reducing  them.  Other  bacteria  are  found  which 
oxidize  hydrogen  sulphide  to  sulphates. 

As  regards  organic  carbon  there  are  two  great  classes  of 
bacteria : 

(1)  Those  which  oxidize  organic  carbon  and  produce  carbon 
dioxide. 

(2)  Those  which  reduce  organic  carbon  and  form  marsh  gas 
and  solid  products.     Bacteria  are  also  found  in  the  soil  which  can 
utilize  carbon  dioxide  and  hydrogen  to  form  organic  matter,  and 
there  are  also  some  which  can  use  marsh  gas.     Bacteria  which 
require  oxygen  are  called  aerobic,  those  which  do  best  without 
oxygen,  anaerobic. 

Ammonification. — A   large   number   of   different  bacteria   and 
molds  are  capable  of  converting  organic  nitrogen  into  ammonia. 
1  Bulletin  94,  p.  193,  Office  Exp.  Sta. 


CHEMICAL    CHANGES  2OQ 

Molds  probably  do  the  larger  portion  of  the  work  in  manure 
heaps  and  very  peaty  soils,  but  in  ordinary  arable  soils  bacteria 
predominate.  Most  of  the  bacteria  which  grow  upon  gelatin  or 
agar  are  ammonifying. 

Bacterium  mycoides,  which  appears  to  be  the  most  im- 
portant, decomposes  albumen  with  the  production  of  ammonium 
carbonate  and  small  quantities  of  formic,  acetic,  and  butyric 
acids,  carbon  dioxide,  and  other  products.  It  requires  the  pres- 
ence of  oxygen;  otherwise  it  reduces  nitrates,  if  present,  to 
nitrites  or  ammonia.  The  optimum  conditions  for  its  activity 
are  a  temperature  of  about  30°,  complete  aeration,  slightly  alkaline 
medium,  and  a  slight  concentration  of  the  nitrogenous  substance 
in  solution. 

The  moisture  and  temperature  conditions  of  the  soil  play  a 
prominent  part  in  determining  the  character  of  the  bacterial  flora, 
and  hence  also  the  character  of  the  chemical  products  formed.  The 
mechanical  and  chemical  constituents  of  the  soil  are  also  of  de- 
cided influence.  Heavy  clay  or  loam  soils  contain  a  greater  num- 
ber and  variety  of  anaerobic  organisms  than  light  sandy  or  sandy 
loam  soils  under  the  same  conditions.  But  aerobic  and  anaerobic 
bacteria  are  found  in  both  kinds  of  soils.  Aerobic  organisms  may 
produce  conditions  favorable  to  the  growth  of  anaerobic 
organisms.  Ammonification  in  the  soil  is  due,  at  times,  to  processes 
partaking  largely  of  the  nature  of  decay,  and  at  other  times  of 
putrefaction.  By  decay  we  mean  the  complete  volatilization  of 
the  organic  matter,  while  in  putrefaction  ill-smelling  bodies  are 
found. 

Study  of  Ammonification. — Ammonification  may  be  studied  in 
culture  solutions,  or  in  soils.  The  former  is  better  adapted  to 
certain  bacteriological  studies,  but  methods  which  involve  the  use 
of  the  soil  approach  more  closely  to  natural  conditions.  In  either 
case,  at  the  end  of  a  definite  period  of  time,  the  extent  of  the  pro- 
cess is  compared  by  an  estimation  of  the  quantity  of  ammonia 
formed. 

Brown,1  for  example,  uses  a  culture  solution  composed  of  10 
1  Iowa  Station  Research  Bulletin  No.  2. 


210  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

grams,  peptone  in  1,000  cc.  distilled  water.  He  shakes  100  grams, 
soil  with  200  cc.  water,  niters,  and  inoculates  100  cc.  of  the 
sterilized  culture  solution  with  20  cc.  of  the  nitrate.  Ammonia 
is  determined  in  the  culture  after  incubation  for  six  or  seven 
days.  When  soil  is  to  be  used  as  a  culture  medium,  100  grams. 
air-dried  soil  are  mixed  with  5  grams,  dried  blood  or  5  grams, 
cottonseed  meal  and  5  grams,  water  and  inoculated  with  20  cc. 
soil  infusion,  and  incubated  as  before. 

Various  conditions  which  affect  the  process  of  ammonification 
can  be  studied  in  this  way,  such  as  the  temperature,  character  of 
medium,  time  of  incubation,  kind  of  bacteria,  etc.  If  pure  cul- 
tures of  different  bacteria  are  compared,  it  is  of  course  necessary 
to  estimate  the  number  of  bacteria  in  the  liquid  used  for  inocula- 
tion, according  to  the  method  already  outlined.  Two  important 
ammonifying  bacteria  are  Bacillus  mycoides,  and  Proteus  vul- 
garis,  but  a  large  number  of  bacteria  take  part  in  this  process. 

The  ammonifying  power  of  the  soil  has  been  defined  by  some 
workers  as  the  quantity  of  ammonia  produced  on  inoculating  a 
definite  quantity  of  a  suitable  culture  medium  with  a  definite 
quantity  of  soil,  and  incubating  under  definite  conditions.  Am- 
monifying power  measured  in  this  way  depends  upon  the  number 
and  activity  of  the  bacteria  in  the  soil  at  the  time  of  inoculation, 
and  will  be  affected  by  anything  which  affects  them,  such  as  the 
soil  temperature,  its  moisture,  kind  and  quantity  of  food  present, 
character  of  soil,  etc.  In  carrying  out  such  tests,  it  is  exceedingly 
important  that  the  soils  studied  be  kept  under  comparable  condi- 
tions as  regards  these  varying  factors,  so  that  only  one  factor,  the 
one  being  studied,  is  variable.  Ammonification  in  soils  is,  how- 
ever, quite  different  from  ammonification  in  solution. 

Nitrification. — Nitrification  takes  place  in  two  stages:  nitrates 
are  first  formed  from  ammonia,  and  then  changed  to  nitrites, 
Two  kinds  of  bacteria  have  been  isolated,  namely,  the  nitrous  and 
the  nitric  organisms. 

The  bacteria  which  oxidize  nitrites  to  nitrates  may  be  isolated 
from  the  soil  without  any  great  difficulty.1  A  solution  is  pre- 
pared as  follows: 

1  Wiley's  Principles  and  Practice  of  Agricultural  Analysis,  Vol.  i. 


CHEMICAL   CHANGES 


211 


Distilled  water 1,000  cc. 

Potassium  phosphate i     gram 

Magnesium  sulphate 0.5     " 

Calcium  chloride trace 

Potassium  nitrite • 0.2  gram 

After  sterilization,  100  cc.  of  the  solution  is  inoculated  with 
about  o.i  gm.  moist  soil.  This  medium  is  unfavorable  to  all 
bacteria  except  the  nitrate  organism.  After  the  nitrate  organism 


Fig.  49.-  Microscopic  appearance  of  nitrous  bacteria.     Winogradski. 

has  developed,  as  shown  by  the  formation  of  nitrates  and  the 
weakening  or  disappearance  of  the  nitrous  acid,  a  few  drops  of 
the  culture  are  diluted  with  sterilized  water,  and  fresh  portions  of 
the  medium  seeded  with  single  drops  of  the  diluted  culture.  Some 
of  these  cultures  will  probably  contain  only  the  nitrate  organism, 
but  at  any  rate,  the  other  bacteria  can  be  eliminated  by  a  few 
more  cultures.  The  purity  is  tested  by  plating  with  a 
drop  from  each  culture.  The  nitrate  organism  does  not 


212 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


grow  on  gelatin  or  agar,  so  that  if  no  colonies  appear, 
the  solution  is  probably  free  from  contaminating  bacteria. 
The  growth  of  these  organisms  produces  scarcely  any  change  in 
the  appearance  of  the  solution.  After  staining  with  coloring 
matter,  the  organisms  may  be  seen  under  the  microscope  as 
minute,  peanut-shaped  bacteria.  They  are  termed  Nitrobacter. 


:-^r  *-..-.$ 


" 


•  ,'.:'- 


-  <:%^A   . 

s*'£s  '*•&*&.**• 

•          5*  ^»'«*  if  ^^ 

^S/^J 


Fig.  50. — Microscopic  appearance  of  nitric  bacteria.     Winogradski. 

The  nitrous  organism,  which  converts  ammonia  to  nitrites,  is 
much  less  easily  isolated  than  the  nitric  organism,  for  the  reason 
that  other  bacteria  will  grow  along  with  it,  and  also  because 
it  does  not  grow  well  on  agar  or  gelatin  plates.  Winogradsky1 
was  finally  successful  in  isolating  it.  He  first  cultivated  the 
bacteria  in  a  medium  of  the  same  composition  as  that  given  above, 
except  the  potassium  nitrite  was  replaced  by  about  2  parts  per 
thousand  of  ammonium  sulphate.  A  little  magnesium  carbonate 
1  Wiley's  Principles  and  Practice,  Vol.  i. 


CHEMICAL    CHANGES  213 

was  also  added.  Silica  medium  was  prepared  by  treating  water 
glass  (sodium  silicate)  with  hydrochloric  acid,  and  dialyzing  in 
distilled  water  until  free  from  salts.  The  solution  of  silica  was 
then  concentrated,  nutrient  salts  added  (in  proportions  referred 
to  above),  and  the  liquid  seeded  with  one  drop  of  the  culture 
mentioned  above.  The  mixture  was  poured  into  a  sterilized 
petri  dish,  and  a  drop  of  a  saturated  solution  of  salt  added  to 
coagulate  the  silica.  This  mineral  jelly  was  very  unfavorable  to 
the  growth  of  any  except  the  nitro-organisms. 

The  bacteria  grow  as  very  small  colonies,  but  on  the  surface 
they  form  a  white  crust.  Stained  with  dye,  and  examined  under 
the  microscope,  they  appear  as  round  or  roundish  organisms. 
Winogradsky  separated  three  varieties  of  nitrous  bacteria :  Nitro- 
somonas  europaea  from  Europe,  Nitrosomonas  javanesis  from 
Java,  and  Nitrosococcus  from  America. 

Study  of  Nitrification. — Nitrification  may  be  studied  in  culture 
solutions,  or  in  the  soil,  and  each  method  has  its  advantages  for 
certain  kinds  of  work. 

A  culture  solution  may  be  prepared  as  follows  i1 

Distilled  water 1,000  cc. 

Ammonium  sulphate 2.0  gram 

Potassium  phosphate I  .o     " 

Magnesium  sulphate 0.5      " 

Ferric  sulphate 0.4     " 

Sodium  chloride 2.0     4< 

To  each  100  cc.  portion,  i.o  gm.  magnesium  carbonate  is  added. 
The  solution  is  inoculated  with  a  small  amount  of  soil,  or  with 
soil  extract,  and  incubated  for  25  to  50  days.  The  quantity  of 
nitrous  and  nitric  nitrogen  is  then  estimated.  This  method  may 
be  used  for  studying  the  effect  of  temperature,  light,  etc.,  or  for 
estimating  the  inoculating  power  of  soils  held  under  different 
conditions.  The  differences  in  the  effect  of  soils  inoculated  into 
different  solutions  will,  of  course,  be  due  to  differences  in  the 
number  and  activity  of  the  organisms  in  them. 
1  Lipman,  Report  New  Jersey  Exp.  Sia.,  1907,  p.  176. 


214  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

If  a  soil  is  to  be  used,1  it  is  mixed  with  a  small  amount  of  am- 
monium sulphate,  cottonseed  meal  or  some  other  nitrogenous 
material,  and  water.  Fresh  moist  soil  may  be  used,  or  air-dry 
soil,  which  is  inoculated  with  other  soil  to  furnish  the  bacteria. 
It  is  hardly  practical  to  sterilize  the  soil  by  heat,  as  this  changes 
its  chemical  character  decidedly.  After  incubation  for  a  period 
of  30  to  50  days,  nitrates  are  estimated  in  the  soil.  Nitrification 
in  the  soil  is  different  from  nitrification  in  solution.  Cottonseed 
meal  added  to  a  soil  will  nitrify,  while  if  added  to  solution,  it  will 
putrify.2 

Nitrification,  ammonification,  and  similar  soil  activities,  may  be 
studied  with  respect  to  the  soil,  or  with  respect  to  the  organisms.3 
Nitrifying  capacity4  may  be  defined  as  the  capacity  of  a  soil  to 
serve  as  a  medium  for  the  growth  of  nitrifying  organisms,  com- 
pared with  a  standard  soil,  both  soils  being  provided  with  equal 
members  of  bacteria  of  the  same  activity,  with  equal  amount  of 
nitrogenous  compounds,  and  kept  under  similar  conditions. 
Nitrifying  power  may  be  defined  as  the  ability  of  a  soil  to  set  up 
nitrification  in  a  soil  or  culture  medium  inoculated  with  it,  and  is 
a  measure  of  the  number  and  activity  of  the  organisms  in  the  soil. 
Similar  terms  may  be  applied  to  other  bacterial  activities. 

Conditions  Favorable  for  Nitrification. — The  conditions  favor- 
able for  the  development  of  the  nitrifying  organisms,  as 
established  by  experiments,  are  as  follows : 

(1)  Suitable  Food. — Potash,  phosphoric  acid,  lime,  sulphates, 
and  carbon  dioxide  appear  to  be  essential. 

(2)  Presence  of  Base. — The  nitric  acid  must  be  neutralized,  as 
the  organisms  will  not  thrive  in  an  acid  medium.     Calcium  car- 
bonate or  sodium  bicarbonate  are  effective.     Too  much  base  is 
injurious. 

(3)  Suitable    Temperature    and    Moisture. — Nitrification    is 
most  active  at  36°.     It  almost  ceases  at  low  temperatures. 

1  Am.  Chem.  Jour.,  1903,  p.  225 

2  Report  North  Carolina  Exp.  Sta.  1902-3,  p.  27. 

3  Stevens  and  Withers,  Proc.  Ass.  Off.  Agr.  Chem.,  1909,  p.  34. 

4  Texas  Bulletin,  106. 


CHEMICAL   CHANGES 


21 


(4)  Absence  of  Strong  Light. — Light  suspends  the  action  of 
the  organisms  and  finally  destroys  them. 

(6)  Freedom  from  Excess  of  Salts. — Ammonia  chloride,  car- 
bonate, calcium  chloride,  or  other  salts  in  excessive  amounts 
inhibit  its  action. 

Physical  Conditions. — The  three  most  important  physical  con- 
dition which  affect  nitrification  are,  looseness  of  the  soil,  tempera- 
ture, and  water  content. 

A  loose  and  porous  condition  of  the  soil  is  more  favorable  to 
nitrification  than  a  compact  condition.  Thus,  a  soil  under  cul- 
tivation allows  more  nitrification  than  the  same  soil  in  pasture. 
Stirring  a  soil  also  favors  nitrification.  For  example.  King 
obtained  the  following  results  in  285  days : 


Nitric  nitrogen  per  acre  foot 

Cultivated 
weekly 

Cultivated 
every  two 
weeks 

Pounds 

326 

218 

323 

441 

387 

Pounds 

326 
213 
I99 
401 
245 

The  temperature  also  has  a  decided  effect  upon  nitrification,  as 
is  shown  by  the  figures  of  King  and  Bertz  obtained  in  27  days, 
expressed  as  nitric  nitrogen  in  parts  per  million  of  soil. 


Temperature 
degrees  F. 


34 
50 
70 
90 


Parts 
per  million 

...  6.5 
•  ••  7-7 
."  14.3 
...  29.1 


Nitrifying  organisms,  like  other  living  things,  have  a  minimum, 
maximum,  and  optimum  temperature  of  existance.  The  mini- 
mum seems  to  be  about  the  freezing  point  of  water,  and  the 
maximum  about  45°  C.,  the  optimum  about  35°  C. 

Production  of  Ammonia  and  Nitrates  in  the  Soil. — The  produc- 
tion of  active  nitrogen  in  the  soil  depends  upon  the  nature  of  the 


2l6 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


soil,  and  the  conditions  surrounding  it.  Nitrification  and  am- 
monification,  if  too  slow,  will  not  provide  the  growing  plant  with 
sufficient  food ;  if  nitrification  is  too  rapid,  the  excess  of  nitrates 
may  be  washed  out  and  lost,  thereby  diminishing  the  productive 
power  of  the  soil. 

The  following  is  an  illustration  of  the  effect  of  moisture : 
EFFECT  OF  WATER  ON  PRODUCTION  OF  ACTIVE  NITROGEN.  1 


Soil  A 
Relative  production  of 

Soil  B 
Relative  production  of 

Nitric 
nitrogen 

Nitric 
and  ammonia 
nitrogen 

Nitric 
nitrogen 

Nitric 
and  ammonia 
nitrogen 

72 
100 
76 

o 
o 

101 
100 
106 
70 
35 

135 
IOO 

189 

16 

18 

104 
IOO 
III 

7° 
60 

ila  "          " 

C/Q    "                " 

o/y 

7/0  "             " 

//V 
o/o  "           " 

9/9 

The  most  favorable  amount  of  water  for  the  production  of 
nitrates  in  the  first  soil  was  3/9  of  its  capacity.  Little  or  no 
nitrification  took  place  when  the  soil  was  very  wet,  though  a  con- 
siderable amount  of  ammonia  was  produced.  Plants  which  grow 
in  swamps  or  saturated  soils  must  secure  their  nitrogen  from  am- 
monia or  organic  bodies. 

Nature  of  the  Soil. — By  the  nature  of  the  soil  is  meant  the 
complex  of  physical  and  chemical  properties  which  make  up  the 
soil  properties.  Which  of  these  properties  are  of  predominating 
influence  in  the  production  of  active  nitrogen,  remains  to  be  ascer- 
tained. 

The  nature  of  the  soil  has  a  decided  effect  upon  the  course  of 
nitrification  within  it.  Different  soils  when  placed  under  similar 
physical  conditions,  and  provided  with  an  equal  number  of 
nitrifying  organisms  and  the  same  food  for  them,  produce  differ- 
ent quantities  of  nitrates.  The  quantity  of  ammonia  and  nitrates 
together  which  is  formed  is  not,  however,  so  different.  The 
following  table  shows  the  differences  in  some  soils  in  the  produc- 
tion of  nitrates  and  ammonia: 
1  Fraps,  Texas  Station  Bulletin  106. 


CHEMICAL   CHANGES 


EFFECT  OF  NATURE  OF  Son,  ON  PRODUCTION  OF  NITRATES 

AND     AMMONIA.1 


Rank  t 

ased  on 

Soil 

Nitric 
nitrogen 

Nitric 
and  ammonia 
nitrogen 

IOO 

42 

O4 

14 

V4 

84 

/o  •  ' 
76  

77 

7O 

We  find  that  while  these  soils  varied  from  100  to  5  in  nitrify- 
ing capacity,  the  production  of  active  nitrogen  (nitrates  and  am- 
monia) varied  only  from  100  to  70.  When  the  production  of 
nitrates  alone  is  considered,  the  soils  vary  greatly,  but  if  nitrates 
and  ammonia  together  are  taken,  the  differences  are  much  smaller. 
If  nitrates  are  much  more  valuable  to  plants  than  ammonia,  these 
differences  are  very  important,  but  if  there  is  little  difference  in 
the  value  of  the  two,  soils  under  favorable  conditions  do  not 
vary  greatly  in  their  power  to  supply  nitrogen  from  the  same 
organic  bodies.  According  to  Russell2  plants  on  cultivated  soils 
probably  absorb  all  their  nitrogen  as  nitrates.  There  is  no  doubt, 
however,  but  that  plants  have  the  power  of  absorbing  ammonia, 
and  that  ammonia  is  present  in  the  soil,  though  ordinarily  it  is 
present  only  in  a  small  quantity. 

Effect  of  Chemical  Additions  to  Soil. — While  carbonate  of  lime 
as  a  rule  accelerates  nitrification,  it  has  little  effect  upon  the  total 
production  of  ammonia  and  nitrates  together.  Its  use  may  result 
in  the  production  of  nitrates  in  excess  of  the  needs  of  the  crops, 
and  consequent  loss  of  fertility  to  the  soil. 

Additions  of  fertilizing  materials  to  the  soil  (acid  phosphate, 
sulphate  of  potash)  may  increase  or  decrease  the  production  of 
nitrates,  but  they  have  little  effect  upon  the  total  active  nitrogen 
produced. 

1  Fraps,  Texas  Station  Bulletin  106. 
'2  Soil  Conditions  and  Plant  Growth,  p.  108. 
15 


2l8  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Nature  of  the  Material. — Some  substances  are  more  easily 
attacked  than  others  by  the  organisms  whose  final  products  are 
nitrates.  While  the  importance  of  this  fact  is  chiefly  to  be  con- 
sidered in  reference  to  organic  nitrogenous  fertilizers,  yet  it  is 
necessary  to  bear  in  mind  that  the  organic  nitrogenous  compounds 
of  the  soil  may  vary  decidedly  in  the  resistance  which  they  offer  to 
the  nitrifying  organisms.  Probably  in  any  soil,  the  less  resistant 
compounds  are  oxidized  first,  and  the  remainder  at  a  decreasing 
rate  from  year  to  year,  so  that  the  effect  is  a  continual  diminish- 
ing of  the  nitrates  produced  for  the  use  of  plants,  unless  measures 
are  taken  to  introduce  fresh  nitrogenous  material  susceptible  to 
nitrification. 

Denitrification. — The  term  denitrification  is  applied  to  the 
destruction  of  nitrates.  If  an  extract  of  stable  manure  is  added 
to  a  solution  of  potassium  nitrate,  and  kept  at  a  favorable  tem- 
perature, the  nitrates  in  time  will  disappear  entirely. 

Under  certain  circumstances  the  nitrates  in  the  soil  are  de- 
oxidized with  the  production  of  organic  bodies,  nitrites,  ammonia, 
or  even  free  nitrogen.  In  the  latter  case  there  is  a  loss  of  nitro- 
gen from  the  soil.  We  have  already  seen  that  the  bacteria  which 
change  organic  nitrogen  into  ammonia  require  oxygen,  otherwise 
they  will  take  oxygen  from  nitrates.  The  conditions  favorable 
for  denitrification  are  as  follows : 

(1)  Insufficient  Oxygen. — In  water-clogged  soils,  or  soils  which 
are  so  compact  that  air  cannot  penetrate  them,  denitrification  will 
take  place. 

(2)  Presence  of  an  Excess  of  Vegetable  Matter. — Cases  are 
known  in  which  a  heavy  application  of  manure  destroyed  the 
nitrates  in  the  soil,  and  produced  a  smaller  crop  than  if  no  manure 
had  been  used.     Some  believe  that  the  denitrifying  organisms 
introduced  with  the  manure  are  the  cause  of  the  denitrification, 
but  as  has  been  pointed  out  by  Waririgton  and  others,  farm  manure 
introduces  into  the  soil  another  factor  of  importance,  namely, 
a  large  increase  in  oxidisable  organic  matter,  and  this  may  favor 
denitrification  both  by  lessening  the  gaseous  oxygen  and  by  tend- 
ing   to    rob    the    nitrates    of    their    oxygen.     Undoubtedly    the 


CHEMICAL   CHANGES  2IQ 

organisms  are  essential  to  the  process,  but  they  cannot  thrive  un- 
less the  conditions  are  favorable  to  their  activity,  whether  they 
are  already  present  in  the  soil,  or  introduced  in  the  manure.  Such 
conditions  are,  either  a  diminished  supply  of  oxygen,  as  by  con- 
solidation of  the  soil  or  by  saturation  with  water,  or  a  very  large 
quantity  of  oxidizable  organic  matter. 

Lipman1  determines  the  "denitrifying  power"  of  a  soil  by  seed- 
ing 10  grams,  of  it  into  100  cc.  of  a  neutral  solution  containing 
definite  amounts  of  nitrates,  dextrose,  citric  acid,  and  nutrient 
salts.  When  the  nitrates  have  disappeared  (in  about  10  days); 
the  total  nitrogen  is  estimated  in  the  solution.  The  percentage  of 
nitrogen  lost  from  the  various  cultures  is  taken  as  a  measure  of 
denitrifying  power  of  the  soil.  The  solution  used  is  as  follows : 

1,000.0  cc.  water 

2.0  grams  magnesium  sulphate 

2.0      "       potassium  phosphate 

i.o      "       potassium  nitrate 

0.2      "       calcium  chloride 

5.0      "       citric  acid 

2.0  drops  10  per  cent,  ferric  chloride. 

Neutralize  while  boiling  with  sodium  hydroxide  and  add  2 
grams  dextrose. 

The  soil  may  also  be  used  as  a  medium  in  which  to  grow  the 
bacteria  for  the  study  of  denitrification. 

Assimilation  of  Nitrates  and  Ammonia. — By  growing  plants  in  the 
solution  of  a  nitrate,  it  is  easily  proved  that  they  have  the  power  to 
absorb  it,  and  as  the  plant  grows  vigorously  (when  other  necessary 
elements  are  present),  the  nitrogen  must  be  in  a  form  to  be 
utilized.  The  nitrate  ion  may  be  completely  removed  from  solu- 
tion when  the  other  nutrients  are  present.  Plants  have  also  the 
power  to  take  up  an  excess  of  nitrates.  Small  amounts  of  nitrates 
are  often  found  in  plants.  An  instance  is  on  record  in  which  corn 
took  up  so  much  that  crystals  of  potassium  nitrate  would  fall  out 
when  the  stalk  was  rapped  on  a  table.  Nitrates  appear  to  be  a 
form  of  nourishment  most  eminently  fitted  to  all  cultivated 
plants.  They  are  easily  and  rapidly  taken  up  by  plants.  All 
1  Report  New  Jersey  Exp.  Sta.,  1907,  p.  179. 


22O  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

compounds  of  nitrogen  placed  in  the  soil  tend  to  change  to 
nitrates. 

The  absorption  of  ammonium  salts  by  the  roots  of  plants 
can  be  shown  in  the  same  way,  as  for  nitrates,  namely, 
by  growing  plants  in  solutions  containing  the  salts.  There 
can  be  no  doubt  that  plants  absorb  ammonia.  To  decide 
whether  ammonium  salts  can  serve  satisfactorily  to  produce 
organic  matter,  is  more  difficult,  since  transformation  of 
the  ammonia  to  nitrates  must  be  excluded.  Hampe  grew 
corn  in  solution  containing  ammonium  salts  and  other 
nutrients,  which  were  repeatedly  changed  to  exclude  nitri- 
fication. The  corn  was  apparently  not  nourished  well  at 
first,  but  later  grew  well.  Kuhn  and  Wagner  obtained 
similar  results.  Muntz  deprived  a  soil  of  nitrates  by  washing, 
fertilized  with  ammonium  salts,  and  took  proper  precautions,  to 
prevent  nitrification.  Corn,  beans,  barley,  and  hemp  attained  a 
normal  development,  and  their  growth  could  only  be  attributed 
to  the  influence  of  the  ammonium  salts  used  as  a  fertilizer.  Other 
experiments  in  the  same  direction  could  be  cited.  We  must  con- 
clude that  ammonium  salts,  as  such,  serve  as  nourishment  for 
plants.1 

Fixation  by  Bacteria. — Besides  the  bacteria  which  fix  nitrogen 
in  connection  with  legumes,  other  nitrogen  fixing  bacteria  occur 
in  the  soil. 

These  bacteria  are  not  easily  isolated,  but  may  be  separated 
by  the  dilution  method.  They  may  also  be  separated  by 
plating.2  The  chief  nitrogen-fixing  bacteria  are  Chlostridum 
Pasteurianum  and  species  termed  azotobacter.  Under  favorable 
conditions,  they  decompose  from  100  to  200  grams  sugar  for 
each  gram  nitrogen  fixed. 

Nitrogen  fixing  power  is  estimated  by  Lipman3  by  inoculating 
loo  cc.  of  the  culture  solution  given  below  with  10  grams  of  soil. 
After  incubating  10  days  at  28""  C.  the  total  nitrogen  is  estimated, 
the  nitrogen  in  a  portion  of  the  original  culture  solution  having 

1  Jour.  Agr.  Science  3,  p.  179. 

2  Bulletin  66,  Delaware  Exp.  Sta. 

3  Report  New  Jersey  Exp.  Sta.,  1907,  p.  181. 


CHEMICAI,   CHANGES  221 

previously  been  estimated;  the  gain  in  nitrogen  is  a  measure  of 
the  nitrogen-fixing  power. 

The  culture  solution  is  prepared  as  follows:  Water  1,000  cc. 
mannite  15  grams;  potassium  phosphate  5  grams;  magnesium 
sulphate  0.2  grams;  calcium  chloride  0.02  gram;  and  ferric 
chloride,  2  drops  of  a  10  per  cent,  solution.  The  solution  is  then 
made  alkaline  with  sodium  hydroxide,  and  sterilized.  Brown  re- 
ports that  much  more  satisfactory  results  may  be  secured  by  the 
use  of  a'soil  as  the  medium  for  the  culture. 

We  have  as  yet  no  evidence  that  the  quantity  of  nitrogen 
assimilated  by  these  bacteria,  is  of  importance  under  ordinary 
agricultural  conditions. 

Experiments  at  the  New  Jersey  Experiment  Station1  indicate 
the  possibility  of  the  addition  of  nitrogen  to  the  soil  in  this  way. 
An  analysis  of  the  soil  at  the  beginning  and  end  of  two  years, 
together  with  the  estimation  of  the  nitrogen  in  the  crops  har- 
vested, showed  an  undoubted  gain  of  nitrogen. 

Assimilation  of  Elementary  Nitrogen  by  Legumes. — The  fact 
that  certain  kinds  of  plants  can  utilize  atmospheric  nitrogen  was 
not  discovered  until  about  1882.  At  that  time,  Hellriegel2 
demonstrated  this  fact  by  experiments  described  briefly  as 
follows : 

Lupine  seed  were  planted  in  pots  of  soil  which  had  been  heated 
sufficiently  to  destroy  all  forms  of  life  in  it,  and  which  had  been 
subjected  to  analysis  so  that  the  exact  amount  of  nitrogen  present 
in  the  quantity  of  soil  taken  was  known.  All  the  pots  were  pro- 
tected from  bacteria  and  watered  with  sterilized  water.  To  one 
series  of  pots,  there  was  added  a  small  amount  of  an  aqueous 
extract  from  a  soil  in  which  lupines  had  grown  well.  To  the 
other  series,  no  addition  was  made.  When  the  plants  were 
grown,  they  were  dried,  and  weighed.  The  quantity  of  nitrogen 
in  the  plants,  and  in  the  soil  remaining  in  the  pots,  was  determined 
by  chemical  analysis.  As  the  nitrogen  originally  present  in  soil 

1  Report  for  1907,  p.  168. 

2  Exp.  Sta.  Record  5,  p.  835. 


222  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

and  seed  was  known,  the  loss  or  gain  of  nitrogen  could  then  be 
easily  calculated.     Some  results  are  as  follows : 


No  addition 

Soil 
extract  added 

Grams 
I  OI 

Grams 
4.O  ^ 

Gain  -I-  or  loss       of  nitrogen  

O  OO7 

I      T     QC 

The  experiment  showed  not  only  that  the  lupine  could  utilize 
the  nitrogen  of  the  air,  but  proved  that  the  soil  extract  contained 
something  which  brought  it  about.  Observations  showed  that 
the  lupines  assimilate  nitrogen  only  when  nodules  are  present  on 
their  roots.  Examination  of  the  nodules  showed  that  they  con- 
tained bacteria,  and  further  experiments,  similar  to  the  one 
described  above,  proved  that  plants  grown  in  soil  inoculated  with 
these  bacteria  evolved  nodules  and  attained  the  power  of 
assimilating  elementary  nitrogen.  By  experiments  similar  to 
those  we  have  described,  it  was  proved  that  alfalfa,  vetch,  clover, 
cow  peas,  and  other  leguminous  plants  have  the  power  of  utilizing 
the  free  nitrogen  of  the  air  when  the  proper  bacteria  are  present ; 
but  corn,  wheat,  oats,  and  most  plants  other  than  legumes,  can 
take  up  only  nitrogen  in  combination. 

Formation  of  the  Tubercles. — When  a  lupine  seed  is  planted  in 
inoculated  soil  free  from  combined  nitrogen,  the  plant  grows 
until  the  nutrient  in  the  seed  is  consumed,  then  ceases  to  grow, 
and  shows  all  signs  of  nitrogen  starvation.  In  the  meantime, 
tubercles  are  forming  on  its  roots.  In  a  few  days,  it  begins  to 
grow  vigorously,  and  appears  to  possess  an  abundance  of  nitro- 
gen. The  tubercles  themselves  pass  through  three  stages.  There 
is  first  vigorous  growth,  producing  the  tubercle  filled  with  large 
numbers  of  small,  rod-like  bacteria;  then  the  bacteria  change  to 
bacteriods,  assuming  a  T  or  Y  form;  and  finally  the  bacteriods 
begin  to  disappear  and  after  a  little  they  are  absorbed  almost  com- 
pletely by  the  substance  of  the  plant  and  the  tubercles  are  left  as 
empty  pouches.  The  plant  begins  to  receive  benefit  from  the 


CHEMICAL   CHANGES  223 

nodules  when  the  bacteria  assume  the  bacteriodal  form.  That  the 
plant  receives  nitrogen  from  the  tubercles  is  shown  by  analyses 
by  Stoklosa1  at  different  stages  of  growth : 

Nitrogen  in 
tubercles 
Lupines  Per  cent. 

Flowering  stage 5.22 

Fruit  forming 2.61 

Plant  mature 1.73 


Fig.  51. — Branched  bacteria  from  a  clover  nodule. 

The  percentage  of  nitrogen  in  the  tubercles  becomes  less  as 
they  grow  older. 

Effect  of  Conditions  on  Tubercle  Formation. — The  conditions 
here  discussed  are:  (i)  nature  of  the  bacteria;  (2)  effect  of 
fertility  of  the  soil;  (3)  effect  of  salts. 

Nature  of  Bacteria. — The  more  active  the  bacteria,  the  less 
quickly  do  they  assume  the  bacteroidal  form;  the  stronger  the 
plant,  the  more  easily  it  causes  this  change.  A  strong  plant  may 
indeed  prevent  the  entrance  of  the  bacteria  into  its  roots  and  con- 
sequently no  nodules  will  be  formed.  The  nature  of  the  bacteria 
seems  to  be  modified  by  the  host  plant.  That  is  to  say,  the 
bacteria  in  the  nodules  of  one  plant  may  not  inoculate  other  plants 
very  well ;  it  may  produce  nodules  upon  them,  but  not  of  such  size 
1  Exp.  Sta.  Record  7,  p.  922. 


224  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

or  ir  such  numbers  as  on  its  parent  plant.  For  example,  the 
alfalfa  tubercle  bacterium  will  not  readily  inoculate  red  clover  at 
first,  but  in  the  course  of  two  or  three  generations,  the  bacterium 
may  become  accustomed  to  another  plant.  It  is  quite  possible, 
however,  that  there  are  several  kinds  of  these  bacteria. 

Effect  of  Salts. — Marchal1  found  that,  in  water  culture,  the 
formation  of  tubercles  on  peas  was  checked  by  solutions  of  the 
following  strengths :  Alkaline  nitrates  0.05  per  cent. ;  ammonium 
salts  0.05  per  cent. ;  potassium  salts  0.05  per  cent. ;  sodium  salts 
0.33  per  cent. ;  calcium  and  magnesium  salts  and  phosphoric  acid 
favored  their  production. 

Effect  of  Fertility  of  Soil. — As  a  general  rule,  the  more  nitro- 
gen can  be  taken  from  the  soil  by  the  plants,  the  less  is  taken 
from  the  air.  Hellriegel  found  that  the  best  development  and 
largest  number  of  tubercles  are  attained  in  a  soil  quite  free  from 
nitrogen,  while  if  the  soil  contains  very  much  nitrogen,  the  forma- 
tion of  tubercles  may  be  entirely  suppressed.  This  is  probably 
due  to  the  fact  that  the  plants  are  too  vigorous  to  allow  the 
entrance  of  the  bacteria.  The  following  examples  are  from  pot 
experiments  with  alfalfa  by  Hopkins.2  The  difference  in  the 
nitrogen  in  the  crops  grown  in  inoculated  and  in  uninoculated  pots 
is  taken  to  represent  the  gain  through  the  agency  of  the  bacteria. 

Gain  per  acre 
Pounds 

No  addition 46 

With  lime 33 

With  lime  and  nitrogen 8 

With  lime  and  phosphoric  acid 55 

With  lime,  phosphoric  acid  and  nitrogen 9 

With  lime  and  potash 38 

With  lime,  potash  and  nitrogen 9 

In  every  case  the  addition  of  nitrogen  to  the  soil  decreases  the 
amount  taken  from  the  air.  It  must  not  be  understood  that  the 
crop  decreases  also.  In  many  cases  the  crop  is  larger,  but  most  of 
the  nitrogen  in  it  comes  from  the  soil  instead  of  the  air. 

1  Exp.  Sta.  Record  13,  1017. 

2  Bulletin  76,  Illinois  Sta. 


CHKMICAL    CHANGES 


225 


How  the  Nitrogen  is  Assimilated. — There  are  three  possibili- 
ties :  ( i )  The  bacteria  secrete  an  enzyme  which  causes  the  plant 
to  assimilate  nitrogen  through  its  leaves;  (2)  the  bacteria 
assimilate  the  nitrogen  and  are  then  consumed  by  the  plant;  (3) 
the  bacteria  assimulate  nitrogen  and  give  it  off  as  soluble  com- 
pounds, which  are  taken  up  by  the  plant. 


Fig.  52.— Nodules  on  the  roots  of  the  soy  bean. 

The  following  facts  are  related  to  these  theories:  (i)  As 
observed  by  Hellriegel,  in  a  medium  free  from  nitrogen  the  plant 
ceases  to  grow  while  the  nodules  are  developing,  then  suddenly 
begins  to  grow  vigorously  as  if  it  had  a  new  source  of  nitrogen. 
(2)  Young  nodules  contain  more  nitrogen  than  old  ones. 


226 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Fig.  53. — Peas  without  nitrogen  (KP)  grow  as  well  as  with  nitrogen 
(KPS)  but  oats  do  not.     Wagner. 


CHEMICAL   CHANGES 


227 


Further,  the  plant  absorbs  the  bacteria,  and  they  disappear. 
(3)  Nobbe  and  Hiltner  found  that  the  stronger  the  plant,  the 
greater  the  resistance  it  offers  to  inoculation,  and  the  sooner  the 
nodules  are  emptied. 

Exactly  how  the  nitrogen  is  transferred  from  bacteria  to  plant 
is  not  known. 

Inoculation  of  Legumes. — When  a  legume  is  planted  in  new 
localities,  the  bacteria  suitable  to  it  may  not  be  present  to  aid  it 


Fig.  54.— Showing  difference  in  the  growth  of  alfalfa  caused  by 
inoculation  with  bacteria.     Illinois  Station. 

in  the  assimilation  of  nitrogen.  The  safest  plan  is  to  inoculate 
the  soil  with  the  proper  bacteria.  There  are  two  methods  of  doing 
this. 

(i)  The  first  method  consists  in  inoculating  with  soil  from  a 
field  where  the  plants  have  been  growing  well.  This  is  the  surest 
method,  but  open  to  some  objections.  Freight  charges  on  the 
soil  may  be  expensive ;  the  soil  may  be  difficult  to  secure ;  injurious 
insects  or  diseases  or  weeds  are  likely  to  be  brought  into  the  soil. 


228  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

(2)  The  second  method1  consists  in  inoculating  the  soil  or  seed 
with  a  pure  culture  of  the  necessary  organisms.  This  method 
was  patented  in  Germany  in  1880,  but  did  not  prove  a  commercial 
success.  The  method  has  been  modified,  and  cultures  are 
now  upon  the  market.  Pure  cultures  of  the  symbiotic 
bacteria  may  easily  be  prepared  by  inoculating  a  suitable 
sterilized  culture  medium  with  the  bacteria.  The  bacteria 
are  sent  in  a  sealed  tube ;  before  inoculating  the  seed  or  soil  their 
number  is  increased  by  allowing  them  to  multiply  in  a  large  quan- 
tity of  water  provided  with  necessary  salts  and  sugar.  The  seed 
are  then  soaked  in  this  liquid,  dried,  and  planted,  or  the  liquid  is 
mixed  with  soil  and  the  soil  distributed  and  plowed  under. 

The  necessary  bacteria  are  so  generally  distributed  that  it  is 
often  unnecessary  to  inoculate  the  soil.  They  grow  not  only  upon 
cultivated  plants,  but  also  on  many  varieties  of  wild  plants. 

Changes  of  Organic  Matter. — The  organic  matter  in  the  soil 
consists  of  the  unchanged  residues  of  plants  and  animals,  and  the 
products  formed  from  them  by  bacteria  and  other  forms  of  life. 
Decay  takes  place  in  two  directions,  according  to  the  presence  of 
an  abundance  or  a  deficiency  of  air. 

In  the  presence  of  an  abundance  of  air,  decay  is  oxidation;  the 
final  products  are  water,  carbon  dioxide,  ammonia,  and  nitrates, 
while  the  mineral  material  is  left  in  forms  which  can  be  assimi- 
lated by  plants. 

In  the  presence  of  little  or  no  air,  decay  is  a  reducing  process, 
oxygen  is  taken  away  from  nitrates,  or  the  higher  oxides  of  man- 
ganese or  rron.  Gaseous  products,  such  as  carbon  dioxide,  marsh 
gas,  hydrogen,  and  free  nitrogen,  are  produced  in  comparatively 
srmll  quantities  and  slowly.  The  organic  material  is  converted 
into  highly  resistant  bodies  which  hold  their  mineral  content  in 
forms  not  assimilable  by  plants.  The  vegetable  matter  is  con- 
verted into  brown  substances,  partly  soluble  in  water  and  impart- 
ing a  brown  color  to  it.  The  compounds  produced  are  acid  sub- 
stances, somewhat  antiseptic  in  nature  and  retard  the  decay  of  the 
vegetable  matter.  The  oxygen  required  for  the  production  of 
1  Progress  in  Legume  Inoculation,  Farmers'  Bulletin  315,  U.  S.  D.  A. 


CHEMICAL   CHANGES 


229 


carbon  dioxide  comes  partly  from  easily  reducible  substances 
containing  it,  partly  from  the  substance  itself.  In  consequence 
of  this  loss  of  oxygen,  the  substance  becomes  richer  in  carbon. 
The  following  analyses1  of  three  samples  of  peat  of  different  ages 
show  this  enrichment  in  carbon : 
PERCENTAGE  COMPOSITION  OF  ASH-FREE  PEAT  OF  DIFFERENT  AGES. 


Brown  peat 
from  surface 

Black  peat 
at  85  inches 

Black  peat 
from  1  70  inches 

57-75 
5-43 
36.02 
0.80 
2.72 

62.02 
5-21 
30.67 
2.IO 
7.42 

64.07 
5-01 
26.87 

4-05 
9.16 

Ash 

The  older  the  peat,  the  richer  it  is  in  carbon  and  also  in 
nitrogen. 

Conditions  of  Decomposition  of  Organic  Material. — Various 
experiments  have  been  made  to  study  decomposition  of  the 
organic  matter  of  the  soil.  Many  experiments  have  been 
carried  out  by  Wollny2  with  the  following  method:  A 
mixture  of  sand  or  earth  and  the  organic  material  was  placed  in 
U  tubes,  moistened  with  water,  and  kept  in  a  constant  tempera- 
ture bath.  The  carbon  dioxide  formed  was  drawn  out  every  24 
hours  and  collected  in  a  solution  of  barium  hydroxide  of  known 
strength.  The  unused  barium  hydrate  was  treated  with  standard 
acid,  and  the  quantity  of  carbon  dioxide  evolved  calculated. 

The  following  are  some  of  the  results  of  these  experiments : 

1 i )  Effect  of  Ratio  of  Organic  Matter  to  Soil. — Varying  quan- 
tities of  powdered  horse  dung  were  added  to  the  same  quantity  of 
sand,  other  conditions  remaining  the  same.     The  oxidation  was 
decreased   when   the   carbon   dioxide    formed   exceeded   certain 
limits,  and  was  less  rapid,  the  greater  the  proportion  of  organic 
substance. 

(2)  Effect  of  Fineness  of  Division. — These  experiments  were 
made  with  peat  and  with  pea  straw  of  different  degrees  of  fine- 

1  Detmer,  Landw.  Versuchs-stat.,  1871. 

2  Die  Zersetzung  d.  Organischen  Stoffe. 


230  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

ness.  The  finer  the  more  difficultly  decomposed  substance, 
the  more  rapidly  it  oxidized.  Easily  decomposed  substances,  pea 
straw  for  example,  did  not  oxidize  more  rapidly  when  finely 
divided. 

(3)  The  Stage  of  Decomposition  of  the  Material. — The  more 
decomposed  the  substance,  the  less  rapidly  it  is  oxidized.     The 
following  figures  are  some  results  of  Wollny: 

Volume  of 

carbon  dioxide 

per  100  volume  of 

soil  atmosphere 

Cattle  manure,  fresh 13-43 

Cattle  manure    8  weeks  old 11.71 

Cattle  manure  20  weeks  old 8. 25 

Peat    0-8    inches  deep 2.93 

Peat    9-19  inches  deep 2.72 

Peat  19-31  inches  deep 2.55 

Peat  31-43  inches  deep 2.39 

Peat  43-55  inches  deep 2.26 

It  is  natural  to  expect  the  more  easily  oxidized  material  to  dis- 
appear rapidly,  and  the  more  resistant  materials  at  a  slower  rate. 

(4)  Chemical  Composition. — Leguminous  straws,  on  account 
of  the  presence  of  more  proteids,  are  oxidized  more  rapidly  than 
cereal  straws.    Waxy  material  hinders  the  decomposition  of  turf ; 
when  it  is  removed  by  extraction  with  ether  or  alcohol,  the  ex- 
tracted turf  is  much  more  rapidly  oxidized  than  the  unextracted. 
Tannic  acid  decreases  oxidation;  rye  straw,  corn  fodder,  and  soja 
bean  leaves  soaked  in  tannic  acid  were  oxidized  less  rapidly  than 
the    untreated    substance.     The    addition    of    plant    food    may 
accelerate  the  oxidation. 

(5)  Animal    residues    oxidize    more    rapidly    than    vegetable 
residues.     Green  materials  oxidize  more  rapidly  than  the  same 
material  dried  and  moistened. 

(6)  The  oxidation  decreases  with  the  supply  of  oxygen,  though 
not  proportional  to  the  supply ;  when  the  supply  decreases  beyond 
certain  limits,  the  oxidation  drops  rapidly. 

(7)  Temperature. — The  relative  effects  of  different  tempera- 
tures is  shown  by  the  following  experiment  on  a  compost  mix- 
ture: 


CHEMICAL    CHANGES  23! 

Temperature.  Relative  amount 

Degrees  C.  of  carbon  dioxide 

10     2.8 

20      ; 15.5 

30    -  •  •  •  36-2 

40     42.6 

50     76.3 

(8)  Moisture. — The  oxidation  goes  on  most  rapidly  at  a  cer- 
tain moisture  content,  which  depends  on  the  material.     Increase 
or  decrease  of  moisture  causes  decreased  oxidation. 

(9)  Character  of  Soil. — The  character  of  the  soil  has  a  great 
effect  upon  the  changes  of  organic  matter.     The  various  factors 
which  affect  the  decomposition  may  support  or  counteract  one 
another,  and  the  effect  is  due  to  the  predominating  quantitative 
relations.     The  easy  permeability  and  more  rapid  warming  up  of 
quartz  sand  are  favorable  to  the  decomposition  of  organic  matter, 
while  its  low  water  capacity  is  a  retarding  factor.     Hence  the 
supply  of  moisture  is  the  controlling  factor  in  organic  decomposi- 
tion in  a  sandy  soil.     In  humid  regions,  the  decomposition  may 
proceed  so  rapidly  in  such  a  soil  that  organic  matter  does  not 
accumulate  to  any  extent.     In  a  dry  climate,  decomposition  pro- 
ceeds more  slowly  than  where  sufficient  moisture  is  present,  but 
more  rapidly  in  a  sand  than  in  other  kinds  of  soil. 

Clay  soils  retain  plenty  of  water,  but  there  is  a  deficiency  of  air, 
and  these  soils  are  essentially  cold.  The  decomposition  of  organic 
matter  in  clays  is  thus  determined  by  the  temperature  and  per- 
meability to  air,  and  proceeds  slowly  under  ordinary  conditions. 
In  humid  regions,  compact  clays  may  exclude  the  air  to  such  an 
extent  that  putrefaction  predominates.  Heavy  rains  may  discon- 
tinue oxidation  in  clay  soils,  and  bring  about  deoxidation  pro- 
cesses, among  them  denitrification. 

(10)  Vegetation. — Oxidation  of  organic  matter  appears  to  go 
on  much  more  rapidly  in  a  bare  soil  than  in  a  soil  covered  with 
vegetation.     A  straw  mulch  decreases  oxidation,  but  not  as  much 
as  a  covering  of  vegetation.     The  following  results  of  Wollny 
illustrate  this  point : 


232 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


AVERAGE  OF  19  SUMMER  WEEKS. 

Volume  of 

carbon  dioxide 

in  1,000  volumes  air 

Under  grass 2.1 

Under  straw  mulch 7.2 

Bare  soil 9.4 

The  thicker  the  plants,  the  greater  their  effect  in  reducing 
oxidation.  The  following  experiment  of  Wollny  show  this  fact : 

Volume  of 
carbon  dioxide 
Number  of  plants  in  1,000  volumes  air 

3  oats  to  o.i  meter 5.0 

6  oats  to  o.  i  meter 3.4 

12  oats  to  o.i  meter 2.3 

24  oats  to  o.i  meter.  '• 1.9 

The  difference  appears  to  be  largely  due  to  the  drying  out  of 
the  soil  by  the  plants. 

A  covering  of  vegetation  thus  conserves  the  organic  matter  of 
the  soil ;  cultivation  and  bare  fallow  decrease  it. 

Value  of  Humus. — The  chief  chemical  action  of  humus  results 
from  its  solvent  action,  and  the  solvent  action  of  the  carbon 
dioxide  which  it  produces  in  its  decomposition.  Water  contain- 
ing carbon  dioxide  has  a  much  greater  solvent  power  on  minerals 
than  pure  water.  This  is  illustrated  by  the  following  experi- 
ments of  Dietrich. 

MINERAL  MATERIAL  DISSOLVED  BY  SOLVENTS. 


Distilled 
water 

Water  con- 
taining carbon 
dioxide 

Gram. 

Gram 

Basalt  

u.u^y 

o  298 

o  012 

0.340 

The  addition  of  humus   (turf)  to  the  soil  increases  its  water 
capacity. 


CHEMICAL,   CHANGES  233 

Water  capacity 
in  volume  per  cent. 

Loam 34.4 

3^  loam  and  X  peat 39-Q 

Sand 11.7 

Sand  ^  and  peat  # 22.7 

Except  with  soils  very  rich  in  humus,  the  greatest  production 
will  be  secured  only  by  extensive  use  of  manures  rich  in  organic 
matter,  or  other  measures  suitable  to  enrich  the  soil  in  humus 
materials. 

Action  of  Carbon  Bisulphide  on  Bacterial  Change.1 — Carbon 
bisulphide  applied  to  the  soil  during  the  growing  season  may 
destroy  or  injure  the  crop,  but  if  it  is  applied  some  time  before 
planting,  it  increases  the  fertility  of  the  soil  to  a  decided  extent. 
Its  action  appears  due  to  its  effect  on  the  soil  bacteria.  In  an 
ordinary  soil,  the  bacteria  have  reached  a  condition  of  equilibrium. 
Carbon  bisulphide  destroys  or  injures  the  bacteria,  and  diminishes 
the  production  of  active  nitrogen.  In  time,  new  bacteria  develop, 
but  along  different  lines,  and  there  occurs  both  an  enormous  in- 
crease in  number  of  bacteria,  and  an  abnormal  predominance  of 
certain  species.  The  bacteria  which  prepare  active  plant  food 
are  more  energetic,  and  the  fixation  of  nitrogen  also  takes  place 
to  a  greater  extent  than  usual.  The  nitrogen  is  at  first  locked  up 
in  the  bacterial  bodies,  and  so  is  useless  to  the  plants,  but  it  be- 
comes active  when  they  decay.  Hence  the  action  of  the  carbon 
bisulphide  is  depressing  if  applied  to  a  growing  crop,  but  it  acts 
like  a  nitrogenous  fertilizer  to  a  succeeding  crop.  After  a  longer 
or  shorter  time,  the  soil  is  more  exhausted  than  it  was  at  first. 
This  is  probably  due  not  only  to  the  rapid  transformation  of  the 
more  easily  decomposed  organic  nitrogen  of  the  soil  into  active 
nitrogen,  but  also  to  the  abnormal  mixture  of  soil  bacteria  due  to 
the  changed  conditions. 

Treating  the  soil  with  toluene,  and  heating  the  soil,  have  similar 
effects  to  carbon  bisulphide.  The  heat,  however,  itself  changes  the 
chemical  composition  of  the  soil,  rendering  both  organic  and  in- 
organic material  more  soluble.  According  to  Russell,2  the  action 

1  Russell,  Soil  Conditions  and  Plant  growth,  p.  114. 

2  Jour.  Agr.  Science  3,  p.  in. 

16 


234  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

of  these  agents  is  due  to  the  destruction  of  larger  forms  of  life 
which  feed  on  the  bacteria  and  so  keep  down  their  number. 

Effect  of  Additions  on  Bacterial  Changes. — Fertilizers,  lime,1 
stable  manure,  and  other  additions  to  the  soil  affect  the  bacteria 
of  the  soil.  In  some  soils,  on  fertilization  with  sodium  nitrate, 
bacteria  develop,  which  change  nitrates  into  ammonia  and  pro- 
tein, and  which  may  affect  decidedly  the  utilization  of  the  nitro- 
gen by  plants. 

Azotobacteria  appear  to  be  dependent  on  the  presence  of  lime 
and  magnesium  carbonates ;  so  much  so  that  it  has  been  suggested 
that  this  dependence  may  be  utilized  for  the  detection  of  the  need 
of  soils  for  lime.  Liming  the  soil  may  thus  increase  the  growth 
of  nitrogen-fixing  bacteria. 

Active  plant  food  may  also  affect  the  bacterial  relations.  Some 
bacteria  have  greater  power  for  securing  their  mineral  nutrients 
than  others.  Additions  of  plant  food  to  the  soil  may  increase 
the  number  and  activity  of  certain  kinds  of  bacteria.  The  bacterial 
life  of  soils  deficient  in  active  plant  food  may  also  be  low. 

Weeds  may  have  an  effect  upon  the  bacterial  relations  of  the 
soil.  Cuizeit,  by  estimating  the  nitrifying  power  of  soils  seeded 
to  oats  alone,  and  to  wild  mustard,  found  that  the  mustard  de- 
creased the  nitrifying  power  of  the  soil,  and  the  differences  per- 
sisted the  following  year.  He  concluded  that  the  unfavorable 
effect  of  weeds  such  as  wild  mustard  was  due  not  only  to  unfavor- 
able effects  on  general  conditions  of  growth,  but  also  to  their 
unfavorable  effects  on  the  bacterial  content  of  the  soil. 

Fixation  of  Phosphoric  Acid  and  Potash  by  the  Soil. — When  a 
solution  of  potassium  chloride  is  brought  in  contact  with  a  soil, 
and  afterwards  subjected  to  analysis,  it  is  found  that  a  portion 
of  the  potash  has  disappeared  from  solution.  This  phenomenon 
is  called  absorption,  or  fixation.  Phosphoric  acid,  organic  matter 
and  other  bodies,  likewise  disappear  from  solution. 

Fixation  may  be  studied  by  bringing  a  weighed  quantity  of  soil 
in  contact  with  a  definite  quantity  of  a  solution  of  known  com- 
position, for  a  definite  time,  shaking  from  time  to  time  and  then 
1  Brown,  Iowa  Research  Bulletin  No.  2. 


CHEMICAL   CHANGES  235 

withdrawing  a  portion  of  the  solution  for  analysis.  By  keeping 
all  conditions  constant  except  the  one  to  be  studied,  we  may 
determine  the  effect  of  (a)  the  nature  of  the  soil,  (b)  the  ratio  of 
soil  to  solution,  (c)  the  concentration  of  the  solution,  (d)  the 
time,  (e)  the  temperature,  and  (/)  the  nature  of  the  salt  used. 
These  are  the  principal  factors  which  affect  fixation. 

Another  way1  of  studying  fixation  is  to  allow  a  solution  of  de- 
finite composition  to  percolate  through  a  column  of  soil,  but  this 
method  is  open  to  the  objection  that  the  solution  afforded  to  dif- 
ferent layers  of  the  soil  is  of  different  composition,  since  it  be- 
comes progressively  weaker  as  it  percolates  into  the  soil.  This 
method  is  in  principle  the  same  as  mechanical  washing  devices, 
in  which  fresh  water  flows  where  the  clean  material  comes  out, 
and  the  dirty  material  enters  where  the  dirty  water  flows  out.- 

Factors  of  Fixation. — The  important  factors  governing  fixation 
are  as  follows : 

(i)  The  Character  of  the  Salt. — Potash,  phosphoric  acid,  am- 
monia, lime,  magnesia,  and  soda  are  fixed  by  the  soil.  Chlorine, 
nitric  acid,  and  sulphates  are  not  fixed  from  strong  solutions ;  but 
from  very  weak  solutions  it  appears  that  some  fixation  may  take 
place. 

That  is  to  say,  if  potassium  chloride,  nitrate,  or  sulphate  in 
solution  are  brought  in  contact  with  a  soil,  a  portion  of  the  potash 
disappears,  but  the  amount  of  chlorine,  nitrate,  or  sulphate  in  the 
solution  remains  nearly  as  it  was  before.  The  potash  is  replaced 
by  an  equivalent  amount  of  lime,  soda,  and  magnesia. 

Different  percentages  are  absorbed  when  potash,  phosphoric 
acid,  etc.,  are  brought  in  contact  with  the  same  soil  in  equivalent 
proportions,  that  is,  in  the  proportion  of  their  combining  weights, 
such  as  ninety-five  parts  of  potash  to  62  parts  soda  and  so  on : 

K20     :     Na20     :     CaO     :     MgO     :     2NH3     :     i/3P2O5 

95  62  56  39  34  47+ 

The  percentages  absorbed  are  not  always  in  the  same  order  for 

1  Schreiner  and  Failyer,  Bulletin  No.  32,  Bureau  of  Soils. 


236  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

different  soils.  We  give,  in  the  following  table,  some  results 
secured  with  100  grams  soil  in  contact  with  250  cc.  solution  con- 
taining 0.07  gram  calcium  sulphate  three  days,  and  equivalent 
quantities  of  the  other  salts: 

Percentage  absorbed1 

N  H3  from  ammonium  sulphate 60 

K.2O  from  potassium  sulphate 55 

Na2O  from  sodium  sulphate 19 

MgO  from  magnesium  sulphate 46 

CaO  from  calcium  sulphate 26 

P2O5  from  sodium  phosphate 17 

SO3  from  sodium  sulphate o 

Cl  from  sodium  chloride o 

All  soils  appear  to  absorb  phosphoric  acid,  potash,  and  am- 
monia; but  lime,  magnesia,  etc.,  are  not  always  absorbed.  For 
instance,  Biedermann2  found  that  two  out  of  nine  soils  absorbed 
lime,  six  absorbed  magnesia,  one  absorbed  sulphuric  acid,  and  all 
absorbed  phosphoric  acid  and  potash. 

The  form  of  combination  has  also  some  effect  upon  the  amount 
of  absorption.  For  example,  if  we  compare  ^different  salts  of 
potash,  such  as  the  chloride,  nitrate,  and  sulphate,  we  find  differ- 
ent amounts  of  potash  absorbed. 

Percentage 
K2O  absorbed 

Potassium  phosphate 57 

Potassium  carbonate 65 

Potassium  chloride 57 

Potassium  sulphate 55 

Potassium  nitrate 51 

(2)  The  Nature  of  the  Soil. — Sands,  as  a  rule,  have  low 
absorptive  powers;  loams  and  clays,  much  higher.  The  absorp- 
tive power  of  the  same  soil  depends  upon  the  substance  used  to 
measure  it.  For  example,  it  is  different  for  potash  and  for  phos- 
phoric acid. 

In  the  following  table,  the  absorptive  power  is  measured  by  the 
percentage  of  ammonia  absorbed  by  50  grams  soil  from  a  solu- 
tion of  one  gram  ammonium  chloride  in  208  cc.  water. 

1  Bretschneider,  Jahresber,  f.  Agr.  Chem.,  1868,  p.  17. 

2  Jahresber,  f.  Agr.  Chem.,  1867,  p.  77. 


CHEMICAL   CHANGES  237 

Soil  Absorptive  power1 

Norfolk  sand 4.0 

Tarboro  sand 9.8 

Norfolk  fine  sandy  loam 10.7 

Durham  sandy  loam 17.5 

Porters  red  clay 17.8 

Cecil  clay 18. 7 

Porters  black  loam 27.5 

The  black  loam  in  question  appeared  to  be  rich  in  organic  mat- 
ter. With  100  grams  soil  to  100  cc.  solution  containing  0.4283 
gram  potash  or  0.3032  gram  phosphoric  acid,  respectively,  Bieder- 
mann  observed  a  variation  in  absorptive  power  from  6.0  to  58.7 
per  cent,  for  potash,  and  3.1  to  82.2  for  phosphoric  acid  in  22  soils. 

(3)  The  Concentration  of  the  Solution. — If  the  ratio  of  soil  to 
solution  is  kept  constant,  the  stronger  the  solution  of  salt  used, 
the  greater  the  total  amount  absorbed,  but  at  the  same  time  the 
percentage  is  less.  That  is,  the  amount  absorbed  does  not  increase 
to  the  same  extent  as  the  concentration  of  the  solution.  The  fol- 
lowing table  illustrates  this  point : 

ABSORPTION2   OF   POTASH   FROM   POTASSIUM   SULPHATE. 


Strength  of  solution 
(Grams  per  liter) 

Grams  absorbed 

(250CC.) 

Per  cent. 

absorbed 

o  4708   •  • 

o  0420   .             ... 

54-5 

I  8840   

°'uy// 

43-5 

47IOO    • 

33-5 

9  42OO    

^•oo^o 

I5'7 

(4)  Effect  of  Temperature. — Increase  of  temperature  some- 
times increases  absorption  of  potash  but  it  always  increases  that 
of  phosphoric  acid,  according  to  Biedermann.  In  the  experiment 
50  grams  soil  was  used  and  100  cc.  solution  containing  0.3032  gram 

P.O.- 

1  Withers  and  Fraps,  North  Carolina  Report,  1902-3. 

2  Bretschneider,  Jahresber,  f.  Agr.  Chem.,  1865,  p.  19. 


238  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Amount  phosphoric  acid  absorbed 

Soil  No.  i 

Soil  No.  2 

0.0065 
0.0941 
0.1768 
0.1389 

O.I07I 
O.II3I 
0.2694 

o.  2405 

-is0   C 

oo      v- 

Seven  additional  soils  gave  similar  results. 

(5)  Ratio  of  Soil  to  Solution. — Keeping  the  strength  of  solu- 
tion constant,  and  increasing  the  weight  of  soil  brought  in  con- 
tact with  it  increases  the  total  absorption,  while  the  absorption 
per  :  gram  soil  decreases. 

(6)  Time  of  Contact. — Peters1   studied  the  time  of  contact, 
using  100  grams  soil  to  250  cc.  of  solution  containing  0.5889 
gram   potash : 

Time  Amount  absorbed  gram 

%  hour 0.1417 

2  hours o.  1571 

4  hours 0.1690 

8  hours 0.1860 

24  hours 0.1990 

14  days 0.2037 

Absorption  of  potash  takes  place  rapidly,  and  is  practically 
complete  in  24  hours.  Similar  experiments  have  shown  that 
•phosphoric  acid  is  absorbed  more  slowly. 

Solubility  of  Absorbed  Material. — Absorbed  material  has  a  low 
solubility  in  water.  Peters-  estimated  it  as  follows:  100  grams 
earth  was  brought  in  contact  with  250  cc.  water  containing  0.5888 
gram  K2O  and  after  24  hours  125  cc.  was  drawn  off  and  replaced 
with  water.  This  process  was  repeated  every  24  hours  for  9 
days,  and  each  extract  was  subjected  to  analysis.  The  absorbed 
potash  is  more  soluble  in  water  than  the  soil  potash,  but  not  very 
soluble — about  i  part  in  28,000  parts  water  under  the  conditions 
of  the  experiment. 


1  Jahresber,  f.  Agr.  Chern.,  1860-1,  p.  7. 
'2  Jahresber,  f.  Agr.  Chem.,  1860-1,  p.  n. 


CHEMICAL    CHANGES  239 

Water  containing  carbon  dioxide  dissolved  in  8  days  about  one- 
third  of  the  absorbed  potash;  acetic  acid,  (i  13),  dissolved  about 
two-fifths;  and  hot  hydrochloric  acid  (1:3  parts  water)  dis- 
solved all  the  absorbed  potash. 

.Replacement  of  Absorbed  Material. — If  a  soil  is  allowed  to 
absorb  one  base,  and  is  then  subjected  to  the  action  of  a  second 
solution,  a  portion  of  the  absorbed  base  will  be  replaced  by  the 
second  base.  Other  bases  in  the  soil  will  also  enter  into  solution. 

For  example,  suppose  a  soil  has  absorbed  potash  from  pot- 
assium chloride.  If  it  be  treated  with  a  solution  of  sodium 
chloride,  some  of  the  soda  wrill  be  absorbed,  and  a  portion  of  the 
absorbed  potash,  and  also  some  lime  and  magnesia  will  enter  into 
solution.  Sodium  nitrate,  ammonium  chloride,  calcium  chloride, 
calcium  sulphate,  magnesium  chloride,  and  other  salts  have  a 
similar  action. 

The  amount  of  potash  displaced  would  depend  upon  the  quan- 
tity present,  and  the  nature  and  concentration  of  the  salt  solu- 
tion. 

Importance  of  Absorption. — Absorption  tends  to  preserve  the 
potash,  phosphoric  acid,  and  ammonia  of  the  soil  from  being 
washed  out.  Soda,  lime,  and  magnesia,  for  which  the  soil  has 
less  attraction,  are  more  easily  washed  out.  The  relative  propor- 
tion of  loss,  will,  however,  depend  upon  the  amounts  of  these 
bases  present  in  the  soil  or  rendered  soluble.  As  we  have  seen 
in  the  preceding  section,  soluble  salts  of  lime,  magnesia,  or  soda 
decrease  the  absorption  of  potash  or  replace  absorbed  potash. 

Absorption  tends  also  to  prevent  loss  of  the  soluble  plant  food 
placed  in  the  soil  in  the  form  of  fertilizers ;  for  nitrates,  however, 
the  soil  appears  to  possess  little  absorptive  power. 

The  practical  importance  of  absorption  lies  chiefly  in  con- 
nection with  the  application  of  soluble  plant  food.  It  is  im- 
portant to  know  whether  soluble  plant  food  applied  to  the  soil  will 
be  washed  out  and  lost.  Nitrates  are  not  absorbed.  Potash, 
phosphoric  acid,  and  ammonia,  as  we  have  seen,  are  fixed  by  the 
soil,  and  as  the  solution  percolates  through  the  soil,  coming  in 
contact  with  fresh  masses,  the  larger  part  of  the  soluble  material 


240  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

is  removed.  Thus,  even  with  a  soil  of  low  absorptive  power,  on 
account  of  the  great  mass  of  soil  which  enters  into  consideration, 
almost  all  the  material  is  absorbed. 

With  a  soil  of  good  absorptive  power,  phosphoric  acid  is  mainly 
retained  by  the  uppermost  layers,  the  first  9  inches ;  with  potash, 
although  the  uppermost  9  inches  contains  chiefly  the  greater  por- 
tion of  the  unused  fertilizer,  a  considerable  amount  penetrates  to 
and  is  retained  by  the  second  and  third  9  inches. 

The  absorptive  power  of  soils  also  enters  into  consideration 
when  the  land  is  to  be  irrigated,  in  which  case  it  is  desirable  to 
know  whether  any  of  the  fertilizer  may  be  washed  out  or  carried 
to  too  great  depth  by  application  of  the  water,  and  how  long  a 
time  should  elapse  before  irrigation  will  cause  a  loss  of  plant  food. 

Some  sandy  soils  have  little  absorptive  power,  and  no  doubt 
losses  of  plant  food  occur  where  heavy  rains  fall  shortly  after 
applications  of  potash  and  soluble  phosphates. 

Cause  of  Absorption. — The  causes  of  absorption  are  different 
for  the  basic  radicles,  potash,  soda,  lime,  magnesia,  etc.,  and  for 
the  acid  radicle,  phosphoric  acid.  It  is  accordingly  necessary  to 
consider  these  two  separately. 

In  offering  an  explanation  for  the  absorption  of  bases,  we  must 
consider  the  following  facts  : 

(1)  The  amount  of  absorption  is  often  related  to  the  quantity 
of  silicates  in  the  soil  decomposed  by  hydrochloric  acid. 

(2)  When  a  base  is   absorbed,   it   is   replaced  by  equivalent 
quantities  of  other  bases.     Treat  a  soil  with  sodium  chloride,  for 
example,  and  the  absorbed  sodium  will  be  replaced  largely  by 
lime,  magnesia,  soda,  and  potash. 

(3)  When  a  soil  is  treated  with  an  acid,  it  loses  its  absorptive 
power   almost   entirely,   but  the   addition   of   calcium   carbonate 
restores  it  in  great  part. 

(4)  Hydrated  oxides  of  iron,  and  aluminum,  hydrated  alum- 
inum silicate,  and  sand  have  slight  absorptive  powers,  but  not 
sufficient  to  account  for  the  absorptive  power  of  soils  containing 
them.     Humus  has  a  comparatively  high  absorptive  power,  but 
the  small  quantity  in  most  soils  will  not  account  for  the  results. 


CHEMICAL   CHANGES  24! 

The  conclusion  is  reached  that  the  absorptive  power  of  soils 
for  bases  is  due  to  the  presence  of  silicates  which  react  with  the 
substance  which  it  will  absorb.  The  reaction  is  reversible.  The 
lime,  soda,  magnesia,  and  potash  of  simple  or  complex  silicates 
enters  into  reaction  with  the  substance  absorbed  by  the  soil,  until 
equilibrium  is  reached  between  the  solution  and  the  reactive  soil 
particles.  We  can  hardly  expect  the  law  of  mass  action  to  be 
followed,  for  the  reason  that  the  absorbing  silicates  are  probably 
mixtures  with  different  reactivity. 

Attempts  have  been  made  to  explain  absorption  as  physical  ad- 
hesion to  the  soil  particles.  While  a  portion  of  the  absorbed  sub- 
stance may  be  held  in  this  way  in  soils  composed  of  fine  particles, 
this  theory  does  not  account  for  the  replacement  of  the  absorbed 
base  by  other  bases,  or  for  the  varying  absorptive  power  of  differ- 
ent soils  of  the  same  physical  composition,  or  for  the  loss  of  the 
absorptive  power  of  a  soil  by  treatment  with  an  acid,  and  partial 
restoration  of  it  by  addition  of  calcium  carbonate. 

Absorption  of  Phosphoric  Acid. — When  a  phosphate  is  brought 
in  contact  with  a  soil,  both  base  and  acid  will  disappear  partly 
from  solution.  The  base  follows  the  laws  of  absorption  as  out- 
lined above.  The  phosphoric  acid  follows  about  the  same  laws, 
but  the  cause  of  the  absorption  is  different,  and  is  due  to  reaction 
with  basic  substances,  such  as  hydrated  oxides  of  iron  and  alum- 
inium, and  carbonate  of  lime,  with  production  of  the  much  less 
soluble  phosphates  of  calcium,  aluminium,  and  iron.  It  is  also 
possible  that  the  phosphates  have  power  to  decompose  some  of 
the  weak  silicates.  Phosphates  are  absorbed  more  slowly  than 
bases. 

Changes  of  Phosphoric  Acid  in  the  Soil. — Calcium  phosphate, 
in  the  presence  of  aluminium  and  iron  hydroxides,  has  a  tendency 
to  change  into  phosphates  of  these  bases,  which  are  much 
less  available  to  plants.  The  calcium  phosphate  dissolves, 
and  the  solution  reacts  with  the  hydroxides  in  question,  forming 
phosphates  which  are  much  less  soluble.  The  presence  of  calcium 
carbonate  will  hinder  the  reaction,  since  it  also  will  react  with  the 
phosphoric  acid  in  solution. 


242  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

PHOSPHORIC  ACID  DISSOLVED. l 

( i  gram  substance  to  400  cc.  water. ) 

Parts  per  million 

From  calcium  phosphate 43 

From  ferric  phosphate 42 

From  basic  ferric  phosphate 33 

From  aluminium  phosphate 58 

From  basic  aluminium  phosphate 4 

Decaying  organic  matter,  by  reducing  ferric  to  ferrous  phos- 
phate, and  perhaps  by  combination  with  the  phosphoric  acid,  tends 
to  render  phosphoric  acid  available. 

The  slow  process  of  weathering  breaks  up  the  complex  silicates 
of  the  soil  grains  and  releases  the  compounds  of  phosphoric  acid 
therein.  At  the  Rothamsted  Experiment  Station,  where  wheat 
has  been  grown  with  various  fertilizers  since  1852,  the  amount  of 
phosphoric  acid  soluble  in  citric  acid  was  as  follows,  on  plots 
that  did,  and  did  not,  receive  phosphoric  acid. 


Pounds  per  acre 


1865 

1881 

1893 

No  fertilizer  ... 

24/1 

TO2 

2O2 

Phosphates  

672 

ly* 

Sri 

I  O^O 

°OO 

The  first  plot  produced  on  an  average  12^4  bushels  wheat  con- 
tinuously, but  the  weathering  was  sufficient  to  maintain  nearly 
constant  the  quantity  of  phosphoric  acid  soluble  in  citric  acid.  In 
the  other  case  (producing  24  bushels  wheat)  the  addition  of 
fertilizers  made  a  considerable  increase  in  the  soluble  phosphates 
present.  The  weathering  of  the  minerals  constantly  releases  the 
phosphoric  acid  inclosed  therein.  In  the  presence  of  decomposable 
compounds  of  iron,  and  aluminium,  there  is  a  constant  tendency 
for  the  phosphoric  acid  to  change  to  less  soluble  forms.  Calcium 
phosphate  is  dissolved  by  the  soil  water,  brought  in  contact  with 
iron  and  aluminium  oxides  and  unites  with  these  to  form  phos- 
1  Bureau  of  Soils,  Bulletin,  41. 


CHEMICAL   CHANGES  243 

phates.  If  calcium  carbonate  is  also  present,  the  distribution  of 
the  phosphoric  acid  will  be  modified  by  the  quantitative  relation 
between  the  fixing  materials,  and  the  change  to  iron  and  aluminium 
phosphates  may  be  reduced  or  even  reversed. 

On  the  other  hand,  decaying  vegetable  matter  may  reduce 
ferric  to  ferrous  phosphates,  with  the  production  of  more  soluble 
bodies. 


CHAPTER  XII. 


SOIL  DEFICIENCIES. 

Any  condition  or  defect  of  the  soil  which  tends  to  prevent  the 
maximum  production  of  crops,  or  to  render  it  unsuitable  for  cul- 
tivation, may  be  termed  a  soil  deficiency.  Soil  deficiencies  may 
be  physical  or  chemical. 

Physical  Deficiencies. — These  are  mentioned  here  merely  for 
the  sake  of  completeness.  As  regards  physical  deficiencies,  a  soil 
may  be  too  porous  or  too  stiff,  too  wet  or  too  dry,  too  cold  or  too 
shallow. 


Fig.  55. — Experimental  plots,  Gottingen,  Germany, 
Agricultural   Institute. 

Cold  soils,  which  are  usually  wet,  when  drained  become  warmer. 
The  depth  of  shallow  soils  may  be  increased  by  plowing  a  little 


SOII,  DEFICIENCIES  245 

deeper  every  year  or  by  subsoiling.  Both  porous  and  stiff  soils 
are  benefited  by  organic  matter,  which  makes  the  former  less 
porous  and  the  latter  less  stiff.  Lime  may  improve  stiff  soils  by 
making  them  more  pulverulent.  Wet  soils  are  improved  by  under- 
drainage.  Dry  soils  may  be  aided  by  frequent  stirring  to  prevent 
evaporation  of  water  from  them,  or  by  irrigation.  Hard  pan  may 
sometimes  be  removed  or  prevented  from  forming,  by  proper 
plowing,  or  subsoiling.  In  some  cases  it  is  profitable  to  use  ex- 
plosives to  remove  it. 

Chemical  Deficiencies. — The  chief  chemical  deficiencies  of  soils 
are  acidity,  alkali  (excess  of  soluble  salts),  deficiency  in  organic 
matter,  deficiency  in  lime,  and  in  available  plant  foods,  phosphoric 
acid,  potash,  or  nitrogen.  These  deficiencies  have  been  dis- 
covered by  means  of  field  experiments,  aided  by  other  methods  of 
experiment. 

Recognition  of  Chemical  Deficiencies. — There  are  three  general 
methods  of  ascertaining  the  probable  chemical  deficiencies  of 
soils : 

1 i )  Field  experiments. 

(2)  Pot  experiments. 

(3)  Chemical  analysis. 

Field  Experiments. — All  soil  theories  must  eventually  be  tested 
in  the  field.  Field  experiments  are,  therefore,  fundamental,  and 
information  secured  by  other  methods  must  eventually  be  brought 
back  to  the  field,  and  stand  the  test  of  actual  crop  production 
upon  the  soil.  The  more  removed  from  field  conditions  the  work 
of  the  investigator,  the  more  careful  he  should  be  to  bring  his 
results  into  relation  with  actual  crop  production.  Unless  tested  in 
this  manner,  theories  may  be  developed  which  are  entirely  too  far 
removed  from  agricultural  conditions. 

Methods  of  making  field  experiments  with  fertilizers  are  out- 
lined in  Chapter  XVI.  Similar  methods  are  used  in  other  experi- 
ments, arranged  according  to  the  information  desired. 

Field  experiments  are  subject  to  vicissitudes  of  weather,  insect 
pests,  variations  in  soil,  etc.,  and  hence  must  usually  be  carried  on 
for  several  years,  or  else  en  an  extensive  scale.  Unexpected 


246 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


variations  are  liable  to  occur,  and  this  fact  must  be  allowed  for  in 
all  consideration  of  the  data. 

Pot  Experiments. — In  pot  experiments,1  plants  are  grown  in 
the  soil  to  be  tested,  various  additions  being  made  to  the  soil 
according  to  the  information  desired.  The  soil  can  be  mixed  until 


Fig.  56. — Pot  experiments.     New  Jersey  Station. 


Fig.  57. — Protection  of  pot  experiments  from  inclement  weather. 
New  Jersey  Station. 

uniform,  and  the  pot  supplied  with  a  favorable  amount  of  water, 
kept  at  a  favorable  temperature,  and  the  crops  protected  from 
damage  by  insects,  birds,  or  storms.     The  conditions  can  be  more 
1  Exp.  Sta.  Record  7,  p.  77;  5,  p.  849. 


SOIL  DEFICIENCIES 


247 


easily  controlled  than  field  conditions,  and  certain  problems  can 
be  much  more  easily  studied.  Conditions  are  relatively  more 
favorable  than  in  the  field,  and  the  relation  between  the  pot  ex- 
periments and  field  results,  must  be  traced  out. 

The  pots  used  vary  much  in  size,  shape,  and  material. 
They  may  be  made  of  glass,  galvanized  iron,  enameled 
iron,  or  earthenware,  and  may  vary  in  size  from  a  few 
inches  in  diameter  to  those  which  cannot  well  be  handled 


» 


Fig.  58. — Pot  experiments.     New  Jersey  Station. 


and  are  imbedded  in  the  ground.  Galvanized  iron  is  open 
to  the  objection  that  the  zinc  may  corrode  and  form 
poisonous  compounds.  An  ordinary  form  of  pot  consists  of  a 
cylindrical  vessel  about  8  inches  in  diameter  and  8  inches  deep. 
It  first  receives  a  layer  of  gravel,  covering  a  metal  or  glass 
ventilating  tube  which  reaches  above  the  top  of  the  pot.  The  soil 
is  placed  on  this,  and  receives  the  desired  additions.  The  seed 


248  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

planted  should  be  of  uniform  size  and  vary  in  moderate  limits  in 
weight,  such  as  41  to  47  mg.  each  for  wheat  grains.  The  seed 
are  often  germinated,  and  the  seedlings  planted.  During  the 
period  of  growth,  the  pots  are  usually  weighed  at  suitable  inter- 
vals, and  sufficient  water  added  to  keep  the  moisture  content  uni- 
form. The  pots  are  kept  in  glass  houses,  in  canvas  houses,  in 
wire  houses,  or  in  the  open  air  on  trucks  which  can  be  run  into 
a  glass  house  for  protection  against  storms.  The  pots  are  also 
buried  in  the  ground  sometimes,  but  the  water  content  of  the  soil 
is  much  less  easily  regulated  under  such  conditions.  Examples 
of  pot  experiments  have  been  given  in  the  text. 

The  following  is  the  method  of  procedure  used  at  the  Texas 
Experiment  Station  :l 

Washed  gravel  is  added  in  sufficient  amounts  to  an  8-inch 
Wagner  pot  to  make  the  total  weight  2  kilograms.  Five  kilograms 
of  soil  are  then  added.  The  soil  is  previously  pulverized  in  a 
wooden  box  with  a  wooden  mallet  until  it  will  pass  a  3  mm.  sieve, 
the  gravel  being  removed. 

The  addition  of  fertilizer  consists  of  2^  grams  of  acid  phos- 
phate, and  10  cc.  of  solution  containing  I  gram  nitrate  of  soda, 
and  T  gram  sulphate  of  potash.  In  later  experiments  I  gram  of 
ammonium  nitrate  was  used  in  place  of  nitrate  of  soda.  If  the 
size  of  the  crop  appears  to  render  it  necessary,  more  nitrate  of 
soda  or  sulphate  of  potash  is  added  to  the  pot,  the  solution  being 
diluted  with  about  200  cc.  of  water. 

The  seed  are  weighed  out  so  that  each  pot  receives  the  same 
amount  of  seed  within  o.i  of  a  gram.  Water  is  added  to  one- 
half  the  saturation  capacity  of  the  soil.  If  this  quantity  is  found 
to  be  too  great,  it  is  afterwards  reduced,  but  this  is  the  case  in 
only  a  few  instances.  The  pots  are  weighed,  placed  on  scales 
three  times  a  week,  and  water  added  to  restore  the  loss  in  weight. 
If  the  plants  need  water  between  weighings,  such  quantity  is 
added  as  appears  necessary.  The  object  of  the  weighing  is  to 
maintain  as  closely  as  possible  a  constant  amount  of  water  in  the 
soil.  These  pots  are  kept  in  a  house  with  glass  roof,  and  canvas 
1  Bulletin  126. 


SOIL  DEFICIENCIES  249 

sides  and  top,  for  protection  against  heat,  storm,  and  insect  pests. 
Wire  basket  experiments1  are  made  in  baskets  of  wire  netting, 
about  3  inches  in  diameter  and  3  inches  high,  filled  with  about  200 
grams  soil,  and  dipped  into  melted  paraffin.  The  surface  of  the 
soil  is  covered  with  paraffined  paper,  excepting  for  an  opening  to 
admit  the  seedlings.  The  pots  are  weighed  daily,  and  the  loss 
of  water  restored.  The  plants  are  grown  for  about  three  weeks. 


Fig-  59-— Construction  of  wire  baskets.    Bureau  of  Soils,  U.  S.  D.  A. 

Since  air  is  excluded  from  the  soil  and  since  the  seedlings  develop 
for  the  most  part  from  the  material  in  the  seed,  these  experiments 
are  more  remote  from  field  experiments  than  ordinary  pot  experi- 
ments ;  still  greater  caution,  therefore,  should  be  exercised  in 
interpreting  the  results.  According  to  the  work  of  the  Rhode 
Island  Station,2  this  method  does  not  give  the  same  results  at 
different  times,  and  the  results  do  not  agree  with  those  obtained  in 
field  practice. 

1  Whitney,  Farmers  Bulletin  No.  257. 
-  Bulletin  131. 
17 


250  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Water  culture  experiments  have  been  previously  described 
(Chapter  II),  and  are  well  suited  to  certain  purposes  of  experi- 
ment. They  have  been  used  to  a  certain  extent  for  studying  soil 
deficiencies,  by  growing  the  plants  in  an  aqueous  extract  of  the 
soil.  Conditions  in  water  culture  are  radically  different  from 
those  in  the  soil,  and  still  greater  caution  must  be  exercised  in 
applying  conclusions  secured  by  this  method  of  experiment  to  the 
soil.  It  is  quite  possible  that  materials  will  be  injurious  in  water 
culture  which  are  innocuous  in  the  soil.  Hence  it  is  necessary 
to  confirm  conclusions  drawn  from  experiments  made  in  this 
way  by  pot  and  field  tests. 

Chemical  Analysis. — Chemical  analysis  can  be  used  for  the 
detection  of  certain  soil  deficiencies,  such  as  acidity,  and  the 
quantity  of  alkali  present.  Chemical  methods  can  also  be  used 
to  form  an  opinion  as  to  the  needs  of  the  soil  for  phosphoric  acid, 
potash,  and  nitrogen,  as  shown  in  Chapter  IX.  Chemical  analysis 
is  also  useful  in  extending  the  conclusions  from  field  experiments 
and  pot  experiments  to  other  soils  under  similar  conditions. 

Acid  Soils. — Acid  soils  contain  free  inorganic  or  organic  acids 
or  acid  salts,  which  therefore  give  it  an  acid  reaction.  In  some 
cases  acidity  is  due  to  the  decomposition  of  the  remains  of  plants 
in  the  soil,  forming  organic  acids,  but  it  may  also  be  due  to  in- 
organic acids. 

The  acidity  of  soils  is  usually  neutralized  by  lime.  A  soil  which 
receives  benefit  from  lime  is  not  necessarily  an  acid  soil,  as  lime 
has  other  effects  than  that  of  correcting  acidity;  it  makes  the 
phosphoric  acid  more  available,  liberates  potash,  increases  nitri- 
fication, and  changes  the  physical  properties  of  the  soil. 

Plants  behave  differently  towards  acid  soils ;  some  receive  bene- 
fit from  liming,  while  others  do  not.  The  Rhode  Island  Experi- 
ment Station1  has  conducted  a  large  number  of  experiments  on 
an  acid  soil,  limed  and  unlimed,  with  the  addition  of  acid  phos- 
phate, muriate  of  potash  and  sulphate  of  magnesia,  and  nitrate  of 
soda  or  sulphate  of  ammonia.  These  experiments,  begun  in  1893, 

1  See  their  reports  and  bulletins;  also  Veitch,  Bulletin  90,  p.  183,  Bureau 
Chemistry,  U.  S.  Dept.  Agr.;  Bulletin  No.  66,  Maryland  Exp.  Sta. 


SOIL  DEFICIENCIES 


251 


were  conducted  upon  permanent  experiment  plots  of  the  Rhode 
Island  Station.  Air  slaked  lime  was  applied  in  1893  to  two  of  the 
plots  at  the  rate  of  5,400  pounds  per  acre, and  1,000  pounds  in  1894, 
and  none  since.  Equal  quantities  of  potash,  phosphoric  acid,  and 
nitrogen  have  been  applied  annually  to  each  plot,  and,  since  1899. 
sulphate  of  magnesia.  Two  of  the  plots  receive  nitrogen  as  sul- 
phate of  ammonia,  and  two  as  nitrate  of  soda.  The  tendency  of 
the  two  plots  which  receive  sulphate  of  ammonia  is  to  become 


Fig.  60.  — Bare  spot  in  barley  caused  by  acid  soil.     Woburn,  England. 

acid,  since  removal  of  the  nitrogen  leaves  sulphuric  acid;  while 
the  latter  two  plots  tend  to  become  basic,  since  the  residue  left 
is  soda. 

Equal  numbers  of  plants  were  set  out  on  each  plot.  A  great 
number  of  different  crops  have  been  grown  at  various  times.  A 
few  results  are  as  follows : 


Plot 
number 

Treatment 

Asparagus 
(pounds) 

Barley 
(pounds) 

Onion 
(pounds) 

Turnip 
(pounds) 

23 
25 
27 
29 

O.O 

3-4 
i.i 

4-7 

0.7 
6.5 

2.6 

7-5 

0.2 

41-5 
24.0 

44-3 

2-5 
35-5 
38.0 
44-0 

Sulphate  of  ammonia  limed 
Nitrate  of  soda  

Nitrate  of  soda  limed  

252 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


The  acid  soils  (Nos.  23  and  27)  give  smaller  yields  with  these 
crops  than  the  limed  soils.  The  nitrate  of  soda  plot,  which,  as 
stated,  has  a  tendency  to  become  basic  on  account  of  the  basic 
residue  left  when  the  nitrogen  is  taken  up,  gives  better  yields  than 
the  ammonium  sulphate  plot,  which  has  a  tendency  to  become 
acid. 

Effect  of  Lime  on  Crops  an  Acid  Soil.1 — Benefited  by  Lime.— 
The  following  gives  the  ascertained  effect  of  lime  on  various 
crops  as  found  by  experiments  such  as  described  above : 


Fig.  61.— Sorghum  on  acid  soil,  (A)  limed  and  nitrate  of  soda,   (B)  unlimed 
and  nitrate  of  soda,  (C)  limed  and  sulphate  of  ammonia,  (D)  un- 
limed and  sulphate  of  ammonia.     Rhode  Island  Station. 

Alfalfa,  asparagus,  barley,  beets,  clover,  celery,  cauliflower,  cur- 
rants, cabbage,  cucumbers,  corn,  lettuce,  mangelwurzel,  onions, 
okra,  oats,  peas,  peanuts,  pepper,  parsnip,  pumpkin,  sorghum, 
salsify,  seed  fruits,  stone  fruits,  squash,  spinach,  sugar  beets,  salt 
bush,  timothy,  and  tobacco. 

1  Wheeler,  Farmers  Bulletin  No.  77,  U.  S.  D.  A. 


SOII,  DEFICIENCIES  253 

Indifferent  to  Lime. — Blackberries,  millet,  potatoes,  rasp- 
berries, rye,  and  red  top  grass. 

Injured  by  Lime. — Cranberries,  cowpeas,  sheep  sorrell,  lupine, 
serradilla,  and  watermelon. 

In  these  experiments,  it  will  be  noted  that  the  plants  were  sup- 
plied with  an  abundance  of  phosphoric  acid,  potash,  and  nitrogen. 
Such  being  the  case,  the  beneficial  effect  of  the  lime  could  not  be 
to  render  potash  or  phosphoric  acid  available.  Other  experi- 
ments showed  that  caustic  magnesia,  or  sodium  carbonate  also 
had  a  good  effect.  These  substances  would  also  neutralize  acidity. 

Detection  of  Soil  Acidity. — The  most  satisfactory  method  of 
ascertaining  whether  a  soil  needs  lime  is  to  determine  the  gain  in 
crop  by  its  application.  It  does  not  necessarily  follow  that  a  soil 
which  responds  to  lime  is  acid. 

The  tests  for  acidity  used  at  present  are  as  follows: 

1.  The  Litmus  Test.1 — The  soil  is  moistened  with  water  and 
brought  in  contact  with  blue  litmus  paper.     If  acid,  the  litmus 
turns  red.     Carbonic  acid  also  reddens  litmus,  but  to  a  less  degree 
that,  an  acid  soil. 

2.  Ammonia  Test.2 — The  soil  is  treated  with  ammonia  water, 
and  if  the  liquid  assumes  a  dark  brown  or  black  appearance,  the 
soil  may  be  acid.     This  test  applies  only  where  the  acidity  is  due 
in  a  considerable  measure  to  acid  organic  substances,  and  may 
not  apply  to  all  sections  of  the  country. 

3.  Salt  Method?. — The  soil  is  shaken  with  a  solution  of  potas- 
sium nitrate  and  the  solution,  after  being  boiled  to  remove  car- 
bonic acid,  titrated  with  caustic  soda  and  phenolphthalein.     Part 
of  the  acidity  is  due  to  formation  of  aluminium  and  iron  chlorides, 
which  are  decomposed  in  the  titration. 

4.  Lime  Water  Method.4 — The  soil  is  treated  with  standard 
lime  water,  evaporated,  taken  up  with  water,  and  the  nitrate  tested 
by    evaporating    it    nearly    to    dryness    with    a    few    drops    of 
phenolphthalein.     If  the  phenolphthalein  indicator  becomes  pink, 

1  See  Circular  No.  71,  Bureau  of  Plant  Industry. 

2  Bulletin  62,  Rhode  Island  Exp.  Sta. 

3  Proceedings  Association  Off.  Agr.  Chem.,  1902. 

4  Jour.  Am.  Chem.  Soc.,  1902,  p.  120. 


254  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

an  excess  of  lime  water  has  been  used.  If  it  does  not  become 
pink,  the  soil  is  still  acid.  A  number  of  tests  are  made,  so  as  to 
ascertain  two  quantities  of  lime  water,  with  one  of  which  the  soil 
is  acid,  by  the  other,  made  alkaline.  This  appears  to  be  a  good 
method. 

Other  Effects  of  Lime. — We  have  already  seen  that  lime  is 
necessary  to  plant  life.  Cereal  grasses  require  from  about  Y\  to 
YZ  as  much  lime  as  potash,  while  leguminous  plants  take  up  as 
much  lime  as  potash,  if  not  more.  Lime  is  usually  considered  as 
present  in  abundance  in  the  soil,  but  it  is  quite  possible  that  some 
soils,  especially  sandy  soils  do  not  supply  a  sufficient  quantity  of 
active  lime  for  the  use  of  certain  leguminous  plants. 

The  following  is  a  brief  summary  of  the  part  which  lime 
(chiefly  in  the  form  of  carbonate)  plays  in  the  soil1 : 

1.  It  flocculates  clay  particles,  making  the  soil  more  crumbly 
and,  with  better  tilth,  more  retentive  of  water  and  more  easily 
penetrated  by  rain. 

2.  It  aids  growth  of  bacteria  which  convert  organic  nitrogen 
to  nitrates,  those  which  assimilate  nitrogen  and  other  bacteria. 

3.  It  neutralizes  acids  and  maintains  the  soil  in  an  alkaline 
condition,  which  is  the  condition  most  favorable  to  the  majority 
of  cultivated  plants. 

4.  It  makes  a  soil  productive  which  contains  relatively  small 
quantities  of  plant  food. 

5.  It  counteracts  the  deleterious  effect  of  an  excess  of  magnesia 
in  the.  soil. 

6.  It  liberates  potash  in  the  soil. 

7.  It  unites  with  phosphoric  acid,  preventing  it  from  forming 
less  valuable  phosphates  of  iron  and  alumina. 

An  excess  of  carbonate  of  lime  may  prove  injurious  to  some 
plants,  notably  grape  vines  and  citrus  plants.  From  eight  to 
twenty  per  cent,  of  lime  may  have  this  effect. 

Carbonates  of  magnesia  may,  to  a  certain  extent,  act  in  the 
same  way  as  lime.  We  have  already  seen  that  it  is  well  for  lime 
1  See  Kellner,  Landw.  Versuchs-stat.,  1896,  p.  210. 


SOIIy  DEFICIENCIES 


255 


to  have  a  certain  ratio  to  magnesia.     An  excess  of  either  lime  or 
magnesia  is  not  desirable. 

Lime  Compounds  in  the  Soil. — Lime  is  found  in  the  soil  as  the 
carbonate,  sulphate,  humate,  and  various  more  or  less  complex 
silicates.  Calcareous  soils  contain  considerable  amounts  of  car- 
bonate of  lime.  It  is  quite  probable  that  some  soils  rich  in  humus 
contain  fair  amounts  of  calcium  humates.  As  a  rule,  the  lime 
is  present  in  the  form  of  silicates,  which  are  more  or  less  resist- 
ant to  the  action  of  acid  and  weathering  agencies. 


Fig.  62.— Distributing  lime.     Ohio  Station. 

Application  of  Lime.1 — Lime  is  applied  to  the  soil  as  (a)  Land 
plaster  or  gypsum,  CaSO4  2H2O  which  has  no  power  to  counter- 
act acidity;  (b)  Quicklime  CaO,  which  is  the  most  active  form  of 
lime.  It  is  usually  slacked  before  it  is  worked  into  the  soil.  It 
soon  takes  up  carbon  dioxide,  and  changes  into  the  carbonate. 
It  is  made  by  heating  the  carbonate,  and  so  is  often  called  burned 
1  Bulletin  159,  Ohio  Station  ;  Wheeler,  Farmers  Bulletin  No.  77. 


256 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


lime,     (c)   Ground  Limestone:    Ground  limestone  is  more  mild 
in  its  action  than  quicklime  and  can  be  used  in  larger  amounts. 
The  finer  it  is  ground,  the  more  effective  it  is. 
CaO  :  56  :  CaCO3  :  100 
Lime  Limestone 

One  hundred  parts  of  pure  limestone  contain  56  parts  lime, 
equivalent  to  56  parts  of  pure  burned  lime,  (d)  Oyster  Shells: 
Oyster  shells  contain  some  plant  food.  They  may  be  applied 
unburnt  and  burnt,  (e)  Marl  contains  less  lime  than  shells.  All 
forms  of  lime  should  be  applied  some  weeks  before  planting. 

Quick  lime  is  applied  as  a  top  dressing  on  land  at  the  rate  of 
200  to  500  pounds  per  acre.  Excessive  applications  of  lime  are 
injurious.  Ground  limestone  is  used  in  larger  quantity,  particu- 
larly when  alfalfa  is  to  be  planted.  One  or  two  tons  per  acre  of 
ground  limestone  may  be  used  every  four  to  six  years;  even  as 
much  as  ten  tons  may  be  applied. 

Lime  Liberates  Potash. — Lime  releases  absorbed  potash,  mak- 
ing it  more  readily  available  to  plants.  Hence  the  lime  would  act 
as  an  indirect  potassic  fertilizer.  Boussingault1  found  the  follow- 
ing amounts  of  potash  and  lime  removed  by  clover  from  a  limed 
and  an  unlimed  soil,  in  Kg.  per  hectare. 


Potash 

lyiine 

Phosphoric 
acid 

Unlimed.   first  year  

26  7 

12  2 

1  1  O 

L/imed   first  year  

Q>   6 

&+•* 

7Q  A. 

24  2 

Unlimed   second  year  

Vo-u 

28  6 

79  2 

7O 

O*'* 

TO?   8 

97.2 

22.9 

It  does  not  follow  from  the  above  experiment  that  the  lime 
"released"  potash.  The  liming  made  conditions  more  favorable 
for  the  clover,  and  a  larger  crop  was  produced,  with  a  heavier 
draft  on  the  soil.  The  availability  of  the  plant  food  was  not 
necessarily  changed  because  more  of  it  was  withdrawn  from  the 
soil. 

It  appears  to  be  generally  conceded  that  lime  releases  potash, 
1  Storer,  Agriculture. 


SOIL  DEFICIENCIES 


257 


though  the  writer  has  been  able  to  find  little  experimental  evidence 
that  such  is  the  case  under  actual  field  conditions.  In  the  section 
on  absorption,  evidence  is  given  that  in  the  laboratory,  lime  and 
other  salts  replace  absorbed  potash. 

Experiments    with    Burned    Lime    or    Ground    Limestone. — In 

experiments  at  the  Pennsylvania  and  at  the  Maryland  Experi- 
ment Station,1  ground  limestone  has  given  better  results  than 
burned  lime.  At  the  Pennsylvania  Station,  lime  was  used  in  a 
four  year  rotation  of  corn,  oats,  wheat,  and  hay,  at  the  rate  of  two 
tons  per  acre  of  burned  lime  every  four  years  or  two  tons  of 
ground  limestone  per  acre  every  two  years.  The  average  yield 
for  20  years  is  as  follows : 


No  lime 

Burned  lime 

Ground 
limestone 

Corn   bushels  per  acre  .-..  •  

AO  Q 

7J.   Q 

•1Q    Q 

16  7 

33-9 

ou<9 

ou-  / 
16  5 

13-9 

1o-y 
II  8 

.LVJ-O 

**«0 

The  burned  lime  injured  the  corn,  oats,  and  hay,  while  the 
ground  limestone  was  of  benefit  to  the  oats,  wheat,  and  hay. 
Analysis  of  the  soil  showed  that  the  soil  receiving  burned  lime 
had  lost  more  nitrogen  than  the  other. 

At  the  Maryland  Experiment  Station,  different  kinds  and 
amounts  of  lime  were  applied  to  various  plots  at  the  beginning  of 
the  experiment.  The  results  of  11  years  test  with  1,400  pounds  of 
burnt  lime,  or  an  equivalent  amount  of  carbonate  of  lime  from 
shell  or  marl,  with  the  rotation  of  corn,  wheat,  and  hay,  are  as 
follows : 


No  lime 

Burned  lime 

Carbonate 
of  lime 

24-5 
10.7 
0.65 

32.0 
II.  0 

0.85 

37-0 
14.1 
1.07 

1  Report  for  1902. 


258  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Here  also  the  carbonate  of  lime  gave  better  results  than  the 
quicklime. 

Salt. — Salt  is  used  to  some  extent  as  an  application  to  the  soil. 
It  acts  as  an  indirect  fertilizer. 

Gypsum  or  sulphate  of  lime  CaSO4  2HX),  is  used  to  a  small 
extent  at  present.  Formerly  it  was  held  in  high  esteem,  but  at 
present,  preference  is  given  to  lime,  limestone,  or  direct  fertilizers. 

Toxic  Substances. — It  is  possible  that  some  soils  may  contain 
injurious  substances  besides  alkali  or  acids.  The  theory  of 
Whitney  and  Cameron,  that  plants  excrete  toxic  substances,  has 
already  been  discussed. 

Sulphur. — The  amount  of  sulphur1  in  plants  has  been  for  a 
long  time  under-estimated.  Recent  work2  has  shown  that  many 
plant  products  (especially  seeds)  contain  much  more  sulphur  than 
was  once  thought.  Most  soils  contain  only  small  quantities  of 
sulphur.  It  is  therefore  quite  possible  that  some  soils  are  deficient 
in  sulphur.  It  is  possible  that  the  sulphates  contained  in  acid 
phosphate  are  often  directly  beneficial  to  plants.  Direct  experi- 
mental evidence  that  such  is  the  case  has  not  yet  been  furnished. 

Alkali  Soils.3 — Alkali  consists  of  soluble  salts.  When  present 
in  the  soil  in  excessive  quantities,  these  salts  interfere  with  the 
growth  of  plants,  or  prevent  their  growth  entirely. 

The  ordinary  "alkali"  salts  are  sulphate  of  soda,  chloride  of 
soda,  and  carbonate  of  soda.  The  salts  first  named,  when  crys- 
tallized in  the  surface  of  the  soil,  appear  as  white  substances, 
and  generally  form  what  is  known  as  white  alkali.  Carbonate  of 
soda  has  a  corrosive  action  upon  vegetable  matter  (usually  found 
in  the  soil)  producing  a  black  solution  or  substance,  and  for  this 
reason  is  called  black  alkali.4  Carbonate  of  soda  is  especially  in- 
jurious, for  it  causes  the  soil  to  become  hard  so  that  water  will 
not  easily  penetrate  it.  It  is  also  more  injurious  to  plants  than 
the  less  corrosive  alkali  salts. 

1  See,  however,  Arendt,  Jahresber,  Agr.  Chem.,  1858,  p.  125. 

2  Withers  and  Fraps,  Report  North  Carolina  Exp.  Sta.,  1902-3,  p.  53. 

3  Alkali  Soils  of  the  United  States,  Bulletin  35,  Bureau  of  Soils. 

4  California  Bulletin  128. 


SOIIv  DEFICIENCIES 


259 


Other  salts  than  those  mentioned  above  may  be  present  in 
alkali.  Calcium  chloride,  for  example,  may  give  the  soil  a  black 
color,  and  have  the  appearance  of  black  alkali,  but  it  is  not  as 
injurious  as  carbonate  of  soda.  Nitrate  of  soda  has  been  found 
in  Colorado  soils.1 

Origin  of  Alkali. — Alkali  conies  originally  from  the  decompo- 


Fig.  63. — Alkali  spot  remaining  in  reclaimed  field,  Utah.     Bureau  of  Soils. 

sition  of  rocks.     In  climates  where  there  is  an  abundance  of  rain, 
and  much  water  passes  through  the  soil,  the  alkali  salts   are 
1  Headden,  Bulletin  178,  Colorado  Station. 


260 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


washed  out  about  as  fast  as  they  are  formed  and  carried  into 
streams,  and  thence  to  the  sea. 

In  arid  climates,  since  the  rainfall  is  not  sufficient  to  wash  out 
the  soluble  salts,  they  accumulate.  As  long  as  these  salts  are  dis- 
tributed uniformly  through  the  mass  of  the  soil,  they  cause  no 


50000 


POUNDS     OF     SALT     PER     ACRE. 

10,000  15,000          £0,000          25,000 


30,000          35,000 


Fig.  64.— Salt  content  of  sandy  land  and  of  gumbo  soil,  before  and  after 

irrigation.     Irrigation  causes  the  alkali  to  rise  to  near  the 

surface  of  the  gumbo  soil.     Bureau  of  Soils. 

injury,  but  the  alkali  may  accumulate  in  the  surface-foot  of  the 
soil,  or  it  may  be  carried  away  to  accumulate  in  another  field. 

When  water  comes  in  contact  with  the  soil,  it  dissolves  the 
soluble  constituents  as   far  as  it  penetrates.     If   afterwards  it 


SOIL  DEFICIENCIES  26l 

rises  and  evaporates,  it  leaves  there  all  the  alkali  which  it  held  in 
solution.  Thus  the  alkali  originally  distributed  through  the  soil 
may  be  concentrated  near  the  surface,  thereby  causing  injury  to 
plants.  Checking  evaporation  by  cultivation,  mulching  or  shad- 
ing the  land  by  crops,  will  check  the  rise  of  alkali.  It  sometimes 
happens  that  the  alkali  is  concentrated  in  the  eleventh  or  twelfth 
foot  of  the  soil.  Under  moderate  irrigation,  the  water  will  not 
penetrate  to  this  depth,  but  excessive  irrigation  will  carry  water 
to  such  depths  as  to  dissolve  the  alkali  in  the  depths  of  the  soil, 
and  evaporation  may  then  bring  it  near  the  surface,  so  as  to  cause 
injury.  Soils  have  the  power  of  elevating  water  to  some  dis- 
tance, through  the  small  spaces  between  the  particles. 

Irrigation  waters,  so  necessary  in  arid  regions,  always  contain 
dissolved  salts.  These  are  left  behind  when  the  water  evaporates. 
If  the  water  is  of  poor  quality,  only  a  few  applications  may  be 
sufficient  to  charge  the  soil  with  alkali.  Even  a  good  irrigation 
water  may  give  rise  to  alkali  if  all  the  salts  it  contains  are  allowed 
to  accumulate  in  the  soil. 

Excessive  irrigation,  without  under-drainage,  gives  rise  to 
alkali.1  This  is  evident  first  in  the  low-lying  lands.  The  excess 
of  water  flows  off  into  them,  and  raises  the  level  at  which  the 
water  saturates  the  soil  (known  as  the  water  table),  until  in  some 
cases,  the  water  comes  to  the  surface.  The  alkali  is  washed  from 
the  higher  ground,  and  the  water  evaporates  in  these  low  places, 
leaving  the  alkali  near  the  surface.  The  land  is  thus  converted 
into  alkali  flats.  '  Even  where  the  water  does  not  come  to  the  sur- 
face, whenever  it  comes  within  such  a  distance  of  the  surface  that 
the  capillary  action  of  the  soil  grains  has  the  power  to  bring  it 
to  the  evaporating  point,  alkali  will  accumulate.  The  constant 
rise  of  the  water  containing  salts  and  the  evaporation  of  the 
water,  leaving  the  salts  behind,  will  accumulate  alkali  even  if  the 
water  in  the  soil  does  not  contain  much  alkali.  Usually,  how- 
ever, such  water  contains  some  alkali. 

Alkali  will  accumulate  at  any  point  where  the  water  constantly 
evaporates,  as  on  the  sides  of  irrigation  canals. 
1  Dorsey,  Bulletin  34,  Bureau  of  Soils. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Fig.  65. — Distribution  of  alkali  in  soils  near  Tempe,  Arizona— less  than 
25  per  cent.,  25  to  50  per  cent,  and  over  50  per  cent. 


Fig.  66. — Distance  to  standing    water  in  soils  near  Tempe,   Arizona — less 
than  10  feet,  10  to  20,  20  to  50  feet.     Compare  Fig.  65.     Bureau  of  Soils. 


SOIL  DEFICIENCIES  263 

Whenever  the  water  table  rises,  in  land  under  irrigation  in  arid 
sections,  to  within  four  or  five  feet  of  the  surface,  it  is  a  sign  of 
danger.  Such  a  rise  means  that  the  water  in  the  soil  is  in  such  a 
distance  of  the  surface  that  the  salts  will  be  constantly  moving 
from  the  reservoir  in  the  soil  water,  and  accumulating  in  the  soil. 
Injury  will  result  if  such  an  action  continues.  The  remedy  is 
drainage. 

The  bulk  of  the  alkali  salts  in  an  arid  region  will  be  usually 
found  some  distance  from  the  surface  of  the  soil,  when  the  water 
table  is  many  feet  below  the  surface.  The  depth  at  which  this 
accumulation  occurs  depends  to  some  extent  upon  the  depth  to 
which  the  rainfall  penetrates.  For  example,  Thomas  H.  Means 
found  that  the  alkali  salts  in  coarse  sands  of  a  certain  district 
were  largely  four  to  eight  feet  from  the  surface,  while  in  sandy 
loam,  in  which  the  rain  can  not  penetrate  so  deeply,  the  alkali 
occurs  at  a  depth  of  three  or  four  feet.  The  rain  dissolves  the 
alkali  and  carries  it  down  into  the  soil.  On  evaporation,  some 
of  the  alkali  returns  to  the  surface,  but  the  bulk  of  the  evapora- 
tion must  take  place  below  the  surface,  for  otherwise  the  alkali 
which  is  washed  down  would  be  brought  up  again. 

Surface  accumulations  of  alkali  salts  take  place  where  the 
ground-water  is  sufficiently  near  the  surface  to  cause  the  bulk  of 
the  evaporation  of  water  to  take  place  at  or  near  the  surface. 
Dissolved  material  from  the  soil,  and  that  brought  in  by  the 
ground-water,  will  be  brought  to  the  surface.  Hence  basin-like 
depressions  surrounded  by  sloping  land  usually  contain  alkali. 

Effect  of  Alkali  on  Plants. — Alkali1  usually  causes  injury  at 
the  base  of  the  trunk,  or  the  root  crown  of  the  plant.  The  bark 
of  green  herbaceous  stems  is  usually  turned  to  a  brownish  color 
for  half  an  inch  or  more,  and  is  soft  and  easily  peeled  off.  The 
rough  bark  of  trees  is  turned  nearly  black,  and  the  green  layer 
turns  brown.  The  plant  either  dies,  or  becomes  unprofitable  to 
the  grower. 

The  amount  of  alkali  which  various  plants  will  stand  depends 
upon  a  number  of  conditions,  among  which  are  the  age  of  the 
1  California  Bulletin  128,  p.  5. 


264 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


plant,  the  character  of  the  soil,  the  composition  of  the  alkali,  the 
distribution  of  the  alkali,  and  other  conditions  which  influence  the 
growth  of  the  plants  themselves.  The  most  injurious  salts  are 
the  carbonates;  the  least  injurious  are  the  sulphates. 

The  California  Experiment  Station1  has  endeavored  to  deter- 
mine the  tolerance  of  various  plants  for  alkali  by  estimating  the 
amount  of  alkali  in  soils  in  which  the  respective  plants  did  well 
or  ill.  The  depth  of  four  feet  was  chosen,  because  the  strata  be- 
low that  depth  contain  little  alkali,  and  because  rainfall  or  irriga- 
tion water  ordinarily  does  not  penetrate  below  that  depth.  The 
total  amount  in  this  depth  must  be  considered. 

The  results  of  these  California  investigations  are  as  follows. 
These  figures,  as  stated,  are  tentative  and  subject  to  change: 

HIGHEST  AMOUNT  OF  ALKALI  IN  WHICH   PLANTS  WERE  FOUND 

UNAFFECTED,  IN   POUNDS  PER   ACRE  TO  THE 

DEPTH  OF  FOUR  FEET. 


Sulphate 
(sodium 
sulphate) 

Carbonate 
(sodium 
carbonate) 

Chloride 
(sodium 
chloride) 

Total  salts 

40,800 
30,640 
24,480 
22,720 
18.600 
17,800 
14,240 
9,600 
9,240 
8,640 
4,480 
3.360 
125,640 
102,480 
11,120 
61,840 
52,640 
52,640 
51,880 
15,120 
5.700 
63.720 

7,550 
2,88o 
1,  1  2O 
1,440 
3,84o 
1,760 
640 
680 
1,360 
470 
480 
160 
18,560 
2,760 
2,360 
9,840 
4,000 
1,760 
8,720 
1,480 
11.300 
2,160 

9,600 
6,640 
800 
2,400 
3.360 
1,360 
1,240 
I.OOO 
1,200 
960 
800 
800 
12,520 
5,760 
760 
9,680 
5,440 
5,440 
2,240 

1,160 
3,160 

45,800 
40,160 
26,400 
26,560 
21,840 
20,920 
16,120 
11,280 
1  1,  800 
10,080 

5,760 
5.760 
156,720 
110,320 
13,120 
81,360 
59,840 
59,840 

62,840 

17,280 

17,000 

63,360 

Olives                      

Ficrc 

rilSa  

Pears  

ppopVipc 

Salt  bush  

Alfalfa  (old)  

Sorghum  

Radish     

Wheat  

L,oughridge,  Bulletin  133. 


SOIIv  DEFICIENCIES 


The  Bureau  of  Soils1  of  the  United  States  Department  of 
Agriculture  divides  soils  into  six  grades,  according  to  their 
average  content  of  soluble  salts  to  a  depth  of  six  feet. 


Percentage  of 
total  salts  in  soil 

Black  alkali 
per  cent. 

Crop   behavior 

Grade  i  

0.0-0.20 

Less  than  0.05 

Common  crops  not  injured  un- 
less salt  is  concentrated  in 
first  foot. 

Grade  2  

0.20-0.40 

0.05-0.  10 

All  crops  will  grow  except  those 
most  sensitive,  but  at  the 
higher  limit  all  except  those 
that  are  truly  resistant  are 
distressed.  Alfalfa  grows  but 
hard  to  get  a  good  stand. 
Sugar  cane,  sorghum  and 
barley  do  well. 

Grade  3  

0.40-0-60 

o.  10-0.  20 

Not  suitable  for  common  crops. 
Usually  devoted  to  pasture. 

Grade  4  

0.60.1.0 

0.20-0.30 

Almost  worthless  for  farming 
or  fruit  growing. 

Grade  5  

1.0-3.0 

Over  0.30 

Worthless. 

Grade  6  

Over  3.0 

Worthless. 

The  quantities  of  alkali  mentioned  above  refer  to  the  total 
quantity  of  soluble  salts. 

Utilization  of  Alkali  Soils.2 — (i)  Growth  of  Resistant  Crops.— 
One  method  of  utilizing  alkali  soils  is  to  grow  crops  which  will 
resist  the  action  of  the  alkali  present.  One  of  the  most  resistant 
crops  is  salt  bush,  which  endures  drouth  as  well  as  alkali,  and  is 
used  for  pasturage,  or  as  a  hay  crop.  Sorghum,  oats,  and  sugar 
beets  have  a  high  resistance  for  alkali,  also  some  varieties  of 
barley,  but  it  is  difficult  to  secure  a  stand  of  these  crops  when 
more  than  0.6  per  cent,  of  the  total  salts  is  present. 

(2)  Treatment  of  Black  Alkali. — Black  alkali,  due  to  sodium 
carbonate,  may  be  converted  into  sodium  sulphate  by  means  of 
gypsum.  The  sulphate  is  much  less  harmful  to  plants  and  the 

1  Dorsey,  Bulletin  35,  p.  24. 

2  Hilgard,  Bulletin  128,  California  Exp.  Sta. 

18 


266 


PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 


Fig.  67. — Orange  grove,  (A)  suffering  from  alkali,  (B)  after  the  alkali  has 
been  driven  down  by  irrigation.     California  Station. 


SOIL  DEFICIENCIES  267 

tilth  of  the  land  is  decidedly  improved.  If  much  alkali  is  present, 
gypsum  alone  will  not  be  sufficient  because  it  does  not  remove  the 
alkali,  but  merely  changes  it  to  another  form.  No  chemical  treat- 
ment is  known  which  will  counteract  the  effects  of  white  alkali. 

(3)  Scraping  the  Surface. — At  the  end  of  a  dry  season,  when 
the  alkali  has  risen  to  the  surface,  it  may  be  scraped  off  and 
carted  away.     This  method  might  be  used  for  small  spots. 

(4)  Flushing  the  Surface. — This  method  consists  in  flooding 
the  land  with  water  and  drawing  it  off  after  a  short  time.     This 
method  can  not  be  used  for  any  soil  in  which  the  water  sinks  in 
rapidly,  because  the  water  will  carry  the  alkali  with  it  into  the 

•soil.     With  rather  heavy,  impervious  soils,  with  the  alkali  largely 
at  the  surface,  the  method  may  prove  successful. 

(5)  Flooding  Without  Drainage. — For  this  method,  the  soil 
must  be  naturally  well  under-drained,  with  the  water  table  several 
feet  below  the  surface.     The  water  used  in  flooding  must  go 
through  the  soil,  and  into  the  drainage.     The  method  employed  is 
to  level  the  field,  and  cover  the  soil  with  water  to  the  depth  of 
several  inches,  the  water  being  held  on  the  soil  by  means  of  dikes 
or  levees  so  that  it  soaks  into  the  soil.     Repeated  flooding  will 
carry    the    alkali    out    in    the    drainage    waters.     As    already 
pointed  out,  this  method  can  only  be  applied  to  soils  which  are 
naturally  well  under-drained,  and  on  which  the  flooding  will  not 
raise  the  level  of  the  water-table  to  a  dangerous  extent. 

(6)  Flooding  and  Drainage.^ — Flooding  together  with  artificial 
drainage  will  reclaim  any  alkali  land;  provided,  of  course,  that 
the  flooding  is  carried  out  often  enough,  and  with  sufficient  water, 
and  provided  that  the  drainage  is  sufficient.     Drainage  is  largely 
a  matter  of  engineering.     The  drains  should  be  at  least  three  feet 
deep;  on  some  soils  four  or  five  feet  is  better.     In  heavy  soils 
they  should  be  from  25  to  100  to  150  feet  apart;  in  sandy  soils 
intervals  of  250  to  300  feet  may  answer  the  purpose. 

Prevention  of  Alkali. — Accumulation   of   an   excess   near  the 
surface  is  most  to  be  feared.     If  the  alkali  is  below  the  root  zone 
of  the  plants  it  can  do  no  damage.     Plants  may  grow  and  do  well 
1  Bulletin  34,  Bureau  of  Soils,  also  Bulletin  44. 


268  PRINCIPLES  OF  AGRICULTURAL,  CHEMISTRY 

with  their  roots  just  above  an  accumulation  of  alkali,  but  if  the 
alkali  rises  to  the  roots,  or  if  deeper  rooting  crops  are  grown, 
injury  will  result. 

In  order  to  prevent  the  rise  and  accumulation  of  alkali,  the 
irrigator  must  keep  the  main  movement  of  the  water  downward 
through  the  soil  and  out  in  the  ground-water.  If  the  water 
movement  is  maintained  in  this  direction,  the  alkali  will  not 
accumulate  in  the  soil.  The  movement  need  not  be  at  all  times 
in  this  direction,  but  the  main  movement  must  be  this  way,  or 
alkali  will  accumulate. 

If  the  main  movement  of  the  water  is  up  through  the  soil, 
alkali  will  accumulate.  In  a  sub-irrigated  soil,  the  movement  of 
water  is  up,  due  to  evaporation  of  water,  and  to  transpiration 
from  the  leaves  of  plants.  Hence,  sub-irrigation  means  an 
accumulation  of  alkali. 

Furrow-irrigation  is  a  kind  of  sub-irrigation.  The  soil  at  the 
top  of  the  furrow  is  irrigated  from  below,  and,  in  this  particular 
part  of  the  soil,  the  movement  of  the  water  and  dissolved  salts 
is  up;  so  that  it  will  accumulate  alkali.  If  furrow-irrigation  is 
used  in  places  liable  to  alkali,  the  soil  should  occasionally  bq 
leveled  and  flooded — sufficiently  often  to  keep  the  main  move- 
ment of  the  water  down  through  the  soil. 

If  flooding  is  practiced,  and  hillocks  occur  which  are  not 
covered  by  the  water,  such  spots  are  sub-irrigated,  and  alkali 
will  accumulate  in  them.  Within  these  hillocks,  the  movement  of 
water  is  upwards,  due  to  evaporation  from  the  surface.  Such 
hillocks  should  be  leveled  before  flooding  begins. 

Anything  which  will  counteract  surface  evaporation  will  aid  in 
keeping  the  main  movement  of  the  water  down  and  through  the 
soil.  The  greater  the  extent  that  evaporation  is  prevented,  the 
less  water  is  needed  for  the  irrigation.  Evaporation  from  the 
surface,  therefore,  should  be  prevented  as  much  as  possible. 
Careful  and  frequent  cultivation  will  produce  a  mulch  which  will 
do  much  towards  checking  evaporation.  Trees  or  crops  on  the 
land  will  also  shade  the  surface  and  check  evaporation. 

If  the  water-table  is  too  near  the  surface,  flooding  must  be 


SOIIy  DEFICIENCIES  269 

more  frequent  or  the  land  must  be  under-drained.  Too  frequent 
flooding  may  keep  the  ground  too  wet,  so  that  under-drainage  is 
really  the  practical  remedy.  Whenever  the  water-table  is  at  such 
a  distance  that  the  capillary  action  of  the  soil  can  bring  water 
from  it  to  the  surface,  there  is  great  danger  of  alkali.  In  such  a 
soil,  the  rise  of  water  from  the  ground  water  is  continuous,  so 
that  more  must  be  used  in  irrigation  to  cause  the  main  movement 
of  the  water  to  be  downwards.  By  lowering  the  water-table  by 
means  of  drainage,  the  water-table  may  be  brought  below  the 
power  of  the  soil  to  elevate  it,  thus  checking  the  movement  of 
water,  and  the  alkali  with  it,  towards  the  surface.  The  right 
depth  for  the  water  table  depends  upon  the  character  of  the  soil. 
In  coarse  sand,  water  may  be  raised  over  five  feet.  It  appears 
possible  that  in  fine  sand,  so  often  found  in  alkali  districts,  water 
may  be  raised  as  much  as  twelve  to  fifteen  feet. 

How  much  flooding  will  keep  the  main  movement  of  the  water 
downward  and  through  the  soil  will  depend,  therefore,  upon  the 
water-table  and  the  character  of  the  soil,  and  the  thoroughness  of 
the  cultivation.  The  composition  of  the  ground-water,  and  the 
composition  of  the  irrigation-water  are  important  factors  to 
consider. 

The  alkali  question  is,  in  many  localities,  largely  a  question  of 
proper  drainage. 

Quantity  of  Irrigation  Water. — The  quality  of  the  irrigation 
water  which  can  be  used  upon  soils  without  injury  depends  upon 
the  kind  of  soil,  the  character  of  the  under-drainage,  the  rainfall 
of  the  area,  and  the  manner  in  which  the  water  is  used.  If  the 
soil  is  easily  penetrated  by  water,  and  well  drained,  water  of 
comparatively  high  mineral  content  may  be  used,  provided  that 
it  is  used  in  such  a  manner  as  to  keep  the  main  movement  of  the 
water  through  the  soil  and  into  the  drainage.  In  humid  regions, 
a  water  containing  more  salts  may  be  used  than  in  arid  regions, 
since  less  water  is  used  and  the  natural  rainfall  will  aid  in  wash- 
ing the  alkali  out  of  the  soils.  With  a  heavy  clay  soil,  however, 
and  especially  if  alkali  carbonates  are  contained  in  the  water, 
there  is  always  danger. 


270  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  limit  of  concentration  of  irrigation  water  has  been  placed 
by  some  authorities  at  2,000  or  3,000  parts  per  million.  With  these 
concentrations,  however,  injury  will  result  if  the  alkali  is  allowed 
to  accumulate,  and  is  not  washed  from  the  soil.  Even  compara- 
tively small  amounts  of  mineral  matter  may  give  rise  to  alkali  in 
time,  if  the  soluble  salts  are  allowed  to  accumulate. 

Thomas  H.  Means1  found  water  containing  as  much  as  8,000 
parts  per  million  of  soluble  salts  used  in  the  Desert  of  Sahara, 
many  of  the  crops  grown  being  quite  sensitive  to  alkali.  The 
Arab  gardens  are  divided  into  plots  about  twenty-feet  square, 
with  drainage  ditches  about  three  feet  deep  between  them.  A 
large  quantity  of  water  is  applied  at  least  once  a  week ;  more 
often,  water  is  applied  twice,  the  check  method  of  irrigation 
being  used.  Thus  a  continuous  downward  movement  of  water  is 
maintained,  and,  since  the  soils  are  light  and  sandy,  they  are  well 
drained,  and  there  is  little  opportunity  for  the  soil  water  to  be- 
come more  concentrated  than  the  water  applied. 

It  is  evident  that  the  more  salts  contained  in  the  water,  the 
better  should  be  the  under-drainage,  and  the  more  freely  the 
water  should  be  used.  On  clay  soils,  the  matter  is  more  difficult. 
Alkali  is  so  hard  to  remove  from  some  of  these  soils,  even  if 
under-drained,  that  it  is  doubtful  if  any  except  water  of  high 
purity  should  be  used  on  such  soils. 
1  Circular  No.  10,  Bureau  of  Soils. 


CHAPTER  XIII. 


LOSSES  AND  GAINS  BY  THE  SOIL. 

Under  natural  conditions,  a  large  portion  of  the  material  taken 
from  the  soil  by  plants  returns  to  it  again.  The  plant  dies  and 
decays.  Droppings  from  animals  which  have  eaten  plants  are 
distributed  on  the  soil.  Nevertheless  there  is  some  loss  of 
material  due  to  leaching.  We  have  seen  that  in  the  weathering 
of  rocks  into  soils,  large  percentages  of  material  are  removed,  but 
this  process  has  taken  long  periods  of  time.  Soils  which  are 
highly  weathered  contain  much  less  plant  food  than  those  less 
weathered ;  this  shows  that  losses  by  percolation  occur  under 
natural  conditions.  Under  cultivation,  there  may  be  much  greater 
losses,  due  to  the  smaller  amount  of  vegetation  on  the  soil  at  cer- 
tain seasons,  and  to  the  removal  of  the  crops. 

Gain  by  Rainfall. — In  Chapter  III  we  saw  that  the  rain  dis- 
solves and  brings  down  small  amounts  of  ammonia,  nitrates,  dust, 
and  other  substances.  The  quantity  of  the  most  important  con- 
stituent, nitrogen,  brought  down  by  the  rain,  has  been  shown  to 
average  about  8.0  pounds  per  acre.  (Chapter  III.) 

Loss  in  Percolation. — Of  the  water  which  falls  on  the  soil,  a 
portion  runs  off,  a  portion  evaporates  or  is  transpired  by  plants, 
and  a  portion  penetrates  through  the  soil,  and  either  reappears  in 
springs,  drains,  wells,  or  seepage  water,  or  else  sinks  deep  into 
the  earth.  This  is  the  percolating  water.  The  water  which  per- 
colates dissolves  some  of  the  material  that  comes  in  contact  with 
it,  thereby  causing  a  loss  of  material.  The  water  contains  silica, 
organic  matter,  potash,  soda,  lime,  and  magnesia,  in  the  form  of 
carbonates,  sulphates,  phosphates,  chlorides,  and  nitrates.  The 
more  important  of  these  constituents,  from  an  agricultural  point 
of  view,  are  the  potash,  phosphoric  acid,  nitrogen,  and  lime. 

The  amount  of  loss  by  percolation  depends  upon  a  number  of 
factors : 

(i)  The  Quantity  of  Percolating  Water. — This  depends  upon 
the  amount  of  rainfall,  whether  the  land  is  bare  or  covered  with 
vegetation,  the  character  of  the  soil,  etc.  Unless  the  rainfall  is 


272  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

sufficient  to  saturate  the  soil,  and  pass  into  the  ground  water, 
there  is  no  percolation.  Plants,  by  withdrawing  water  from  the 
soil  and  causing  it  to  evaporate,  diminish  the  quantity  which 
percolates.  As  more  of  the  rainfall  will  penetrate  an  open, 
porous  soil  than  a  compact  soil,  there  would  be  a  greater  surface 
off-flow  from  the  latter.  Soils  which  retain  water  near  the  sur- 
face suffer  greater  losses  by  evaporation.  See  Chapter  VII. 

(2)  The  Composition  of  the  Soil  Extract. — This  depends  upon 
the  fixing  power  of  the  soil  and  the  solubility  of  its  constituents. 
It  also  depends  on  the  kind  and  quantity  of  the  various  additions 
made  to  the  soil.     The  application  of  fertilizers  almost  always  in- 
creases the  quantity  of  potash  and  nitrogen  in  the  soil  extract  and 
consequently  increases  the  loss  of  plant  food.     Ammonium  sul- 
phate and  potash  salts  also  increase  the  quantity  of  lime  in  the 
soil  extract. 

(3)  The  Presence  or  Absence  of  Vegetation. — Besides  affect- 
ing the  amount  of  percolation,  vegetation  withdraws  plant  food 
from  solution  and  thereby  diminishes  the  loss  in  percolating  water. 

Study  of  the  Loss. — The  loss  by  percolation  may  be  studied  in 
two  ways,  both  of  which  have  their  limitations : 

(i)  By  determination  of  the  amount  and  composition  of  the 
percolating  water.  For  the  purposes  of  this  experiment,  a  sec- 
tion of  the  soil  must  be  enclosed  in  a  water-tight  receptable,  so 
arranged  that  all  the  water  which  percolates  may  be  collected, 
measured,  and  subjected  to  analysis. 

A  section  of  soil  in  its  natural  condition,  may  be  isolated  by 
trenches,  enclosed  by  brick  walls,  and  then  separated  from  the  sub- 
soil, so  that  the  percolating  water  may  be  collected  in  a  suitable 
vessel.  This  was  the  method  used  in  preparing  the  drain-gauges 
(as  they  are  called)  at  Rothamsted.  See  Chapter  VII. 

Soil  may  also  be  placed  in  boxes  of  cement1  or  cans  of  gal- 
vanized iron,  or  other  material,  arranged  with  suitable  tubes  and 
collecting  vessels.  In  such  case,  the  soil  is  stirred  and  aerated 
and  is  otherwise  under  unnatural  conditions.  The  apparatus 
1  New  York,  Cornell  Station  Report,  1909. 


LOSSES  AND  GAINS  BY  THE  SOIL, 


273 


should  be  left  for  sufficient  time  to  allow  readjustment  to  take 
place. 

All  the  water  which  falls  on  the  soil  in  such  an  apparatus  must 
either  percolate  or  evaporate.  The  percolation  will  therefore  be 
in  excess  of  that  in  a  free  area,  where  a  portion  of  the  water  runs 
off. 

(2)  The  second  method1  consists  in  determining  the  quantity 
and  composition  of  the  water  from  tile  drains  in  the  field.  Tile 
drains  run  when  the  water  does  not  pass  into  the  subsoil  rapidly 
enough  to  keep  the  soil  from  becoming  saturated  in  the  vicinity 
of  the  drains.  The  quantity  of  drain  water  does  not,  therefore, 
represent  the  quantity  of  water  which  percolates,  but  its  com- 
position should  represent  to  a  certain  extent  the  composition  of 
the  percolating  waters. 

Quantity  of  Loss  by  Percolation. — The  composition  of  the 
drainage  water  from  some  of  the  plots  at  Rothamsted2  is  given 
in  the  following  table : 

ANALYSIS  OF  DRAINAGE  WATERS  IN  PARTS  PER  MILLION. 


Rothamsted 

Phosphoric 
acid 

Potash 

Nitric 
nitrogen 

Lime 

QQ   T 

Ammonium  salts  only  
Ammonium   salts    and    super-phos- 

1.44 

i  66 

-/ 

i-9 

•9 

13-9 

90.1 
I54-I 

T^C     fi 

Full  mineral  dressing  and  ammonia 

o  91 

2.9 

1o-o 
14.0 
16  i 

l8l.4 

•4 

14/.4 

[f  we  assume  a  downward  percolation  of  10  inches  of  drain- 
age water,  i  part  per  million  of  water  corresponds,  in  round  num- 
bers, to  2l/4  pounds  per  acre  per  annum.  According  to  this 
estimate,  from  il/2  to  334  pounds  phosphoric  acid,  2l/2  to  i2l/2 
pounds  potash,  and  9  to  36  pounds  nitrogen  are  lost  in  the  drain- 
age waters  a  year,  according  to  the  condition  of  the  soil. 

At  Rothamsted,  the  average  amount  of  nitrogen  contained  in  the 
crops  (wheat)  in  30  years  on  the  unmanured  plots  was  18.6  and 
20.3  pounds ;  the  estimated  loss  by  drainage  from  tiles,  10.3  and 

1  Jour.  Agr.  Sci.,  1906,  p.  377. 

2  Hall,  An  Account  of  the  Rothamsted  Experiments,  p.  237. 


274  PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

12.0  pounds  respectively,  with  an  estimated  gain  of  5.0  pounds 
nitrogen  derived  from  rain  and  dew.  From  2/9  to  *4  of  the 
total  loss  of  nitrogen  passes  into  the  drainage  waters. 

Gains  by  Material  Dissolved  in  Capillary  Water. — A  certain 
portion  of  the  water  which  sinks  into  the  subsoil,  rises  again  to 
be  evaporated  near  the  surface  or  transpired  by  plants.  It  has 
been  claimed  that  this  water  may  bring  dissolved  material  to  the 
surface  soil.  Such  is  indeed  the  case  in  arid  regions  where 
soluble  salts  are  within  reach  of  the  water.  The  alkali  zone  may 
rise  or  sink  to  some  extent  with  the  dry  or  wet  character  of  the 
season.  In  humid  sections,  however,  material  is  dissolved  by  the 
water  as  it  passes  through  the  surface  soil,  and  the  gain  can  be 
due  only  to  a  longer  contact  with  the  subsoil.  There  may  be  some 
gain  of  this  kind,  but  it  would  have  to  be  considerable  to  counter- 
balance the  material  dissolved  in  soil  water  which  enters  the 
ground  water  and  does  not  return  to  the  surface.  The  writer  has 
been  able  to  find  no  experimental  data  showing  the  relative 
solubility  of  the  material  of  soils  and  subsoils,  and  the  relative 
quantity  of  water  which  reaches  the  subsoil  and  which  returns  to 
the  surface. 

Losses  by  Washing. — Water  running  off  on  the  surface  carries 
soil  particles  with  it,  so  that  as  a  general  rule  the  surface  soil  is 
deeper  in  valleys  and  thinner  on  hill-sides.  The  particles  are  car- 
ried to  some  extent  in  the  water  of  streams,  and  may  be  deposited 
elsewhere  along  the  course  of  the  stream,  or  carried  to  the  sea.  In 
regions  of  heavy  rapid  rains,  the  running  water  may  cut  ravines 
and  gullies,  and  practically  destroy  unprotected  hillside  land. 
Vegetation  is  a  protection  against  such  loss,  and  so  is  anything 
which  checks  the  rapidity  of  the  flow  of  the  water.  Proper  hill- 
side terracing  is  the  best  treatment  for  cultivated  land. 

Loss  by  Bacterial  Action. — The  losses  by  bacterial  action  fall 
on  the  organic  matter  and  the  nitrogen  of  the  soil,  none  of  the 
other  materials  being  directly  lost  in  this  way.  Excessive  nitri- 
fication is  followed  by  losses  of  nitrogen  as  nitrates  in  the  drain- 
age water,  usually  as  calcium  nitrate,  which  involves  a  loss  of 
lime,  also.  Nitrogen  is  also  lost  to  the  soil  by  denitrification,  par- 


BOSSES  AND  GAINS  BY  THE  SOIL  275 

ticularly  when  the  soil  is  water-logged  or  receives  excessive 
quantities  of  manure.  Considerable  losses  of  nitrogen  take  place 
in  cultivated  soils. 

Organic  matter  is  lost  from  all  cultivated  soils  by  oxidation. 
The  factors  which  influence  the  oxidation  of  organic  matter  have 
been  discussed  in  a  previous  chapter. 

Gains  of  Nitrogen  by  Bacterial  Action. — Considerable  amounts 
of  nitrogen  may  be  assimilated  by  legumes  in  connection  with 
bacteria.  Crimson  clover,  according  to  the  New  Jersey  Station, 
may  take  up  200  pounds  nitrogen  per  acre  per  year.  Similar 
studies  at  the  Delaware  Station1  with  various  legumes  showed 
the  yields  to  range  from  31  to  140  pounds  nitrogen  per  acre. 
Velvet  beans  gained  213  pounds  per  acre  in  Alabama  experiments, 
172  pounds  in  Louisiana,  and  141  pounds  nitrogen  in  Florida. 
Cowpeas  gained  70  pounds  in  Alabama,2  and  35  per  cent,  was 
left  in  leaves  and  stubble  if  the  vines  were  mowed.  Like  results 
with  other  legumes  showed  an  average  gain  of  122  pounds 
nitrogen  per  acre  for  sixteen  States. 

It  is  believed  by  some  that  appreciable  quantities  of  free  nitro- 
gen may  be  fixed  by  soil  bacteria,  which  have  no  connection  with 
legumes,  especially  when  the  soil  receives  manure  or  other 
vegetable  matter  for  the  bacteria  to  feed  upon.  This  subject 
requires  further  investigation.  Bacteria  which  have  this  power 
are  certainly  present  in  the  soil,  but  to  what  extent  they  aid  in 
maintaining  the  supply  of  combined  nitrogen  in  the  soil,  is  not 
known. 

Losses  in  Cropping. — This  is  due  to  the  removal  of  plant  food 
in  that  portion  of  the  crop  which  is  taken  from  the  land.  The 
amount  lost  in  this  way  varies  largely,  depending  on  (a)  the  size 
of  the  crop,  (b)  the  kind  of  crop,  (c)  the  portion  of  the  crop 
removed,  and  (d)  the  treatment  of  the  residual  portion,  besides 
the  various  factors  which  influence  the  amount  of  plant  food 
taken  from  the  soil  by  the  crop. 

The   fact  that   the   amount   of   plant   food   removed   depends 

1  Bulletin  No.  60. 

2  Bulletin  No.  120. 


276 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


largely  on  the  size  of  the  crop,  requires  little  discussion.  The 
plant  food  removed  varies  largely  with  the  kind  of  crop.  The 
following  figures  show  the  relative  amounts  of  plant  food  re- 
moved by  a  portion  of  different  crops.  These  figures  are  from 
average  values ;  indivdual  analyses  may  vary  somewhat. 

The  quantity  of  plant  food  removed  by  the  marketed  portion  of 
various  crops  of  the  size  named,1  is  as  follows : 
POUNDS  OF  PLANT  FOOD. 


Phosphoric 
acid 

Nitrogen 

Potash 

Corn   40  bushels  (corn  and  cob)  

•78  o 

\VheEt    2*5  bushels  

T  1  O 

1v5-u 

i^.u 

y.u 

Cotton  lint  (250  pounds)  

O   I 

^5.0 
o  8 

.u 

98  o 

181  o2 

/^.u 

T  r  Q 

14^5.  u 

1^.  u 

17  O 

1oo-u 

72  O 

Rice    i  ooo  pounds  

O/-^ 
12  O 

/^.<J 

/^•u 

«3»w 

.u 

Loss  in  By-Products. — The  by-products  consist  of  the  straw, 
chaff,  cottonseed,  etc.,  and  the  loss  of  plant  food  depends  upon 
how  they  are  disposed  of.  If  they  are  removed,  and  sold,  or 
otherwise  taken  away,  all  the  plant  food  in  them  is  lost.  If 
burned  and  the  ashes  returned  to  the  soil,  the  nitrogen  is  lost.  If 
turned  under,  the  loss  is  much  less.  If  made  into  manure,  which 
is  afterwards  placed  in  the  soil,  there  is  still  some  loss. 

PLANT  FOOD  IN  BY-PRODUCTS  OF  THE  CROPS  IN  PRECEDING  TABLE. 


Phosphoric 
acid 

Nitrogen 

Potash 

Cotton  seed  (  500  pounds)  

16 

Q 

5 

32 

2  3 

29 

Oat  straw  

:3 

14 

Rice  straw  

X4 

37 

1  Bulletin  No.  125,  Texas  Station. 

2  A  portion  of  this  nitrogen  comes  from  the  air. 


LOSSES  AND  GAINS  BY  THE) 


277 


Loss  of  Various  Cropping  Systems. — When  a  soil  is  continu- 
ously cultivated  to  the  same  crop,  such  as  wheat,  and  all  the 
material  removed,  it  decreases  in  productiveness,  until  it  reaches 
a  low  crop  level,  at  which  production  may  be  maintained  for  a 
number  of  years. 

If  the  soil  receives  fertilizers  or  manure  continuously,  the  losses 
of  plant  food  will  be  greater,  and  the  soil  will  adjust  itself  to  a 
higher  level  of  productiveness  as  long  as  conditions  are  so  main- 
tained. 

Distribution  of  the  Losses  of  Nitrogen. — At  Rothamsted,  study 
was  made  of  the  disposition  of  the  nitrogen  added  to  the  soil  dur- 
ing a  period  of  50  years.  Analyses  were  made  of  soil  from 
different  plots  treated  differently,  at  the  beginning  and  end  of 
the  period,  of  the  crops,  and  of  the  water  from  tile  drains. 
Of  86  pounds  nitrogen  added  per  acre  per  year  in  50  years,  the 
disposition  seemed  to  be  as  follows : 

DISPOSITION  OF  NITROGEN,  PER  YEAR.1 


Average 

Maximum 

Minimum 

r6  7 

2C  o 

8  O 

7  6 

z^.u 

TO      C 

30 

/.u 

26  7 

A-*'0 

-7T     O 

.u 
IQ  O 

•jc  O 

Jl.O 
A  A    Q 

26  o 

oo-u 

The  maximum  loss  took  place  with  ammonium  salts  alone.  The 
amount  of  the  total  loss  was  estimated  by  adding  the  amount  of 
nitrogen  in  the  soil  at  the  beginning  to  the  total  amount  added  as 
a  fertilizer  and  subtracting  from  this  the  amount  present  in  the 
soil  at  the  end  of  the  fifty  years.  The  nitrogen  lost  may  have 
passed  into  the  ground  water  below  the  drains.  In  this  work, 
only  17  per  cent,  of  the  nitrogen  was  used  by  the  crop.  It  is 
quite  possible  that  with  smaller  applications  of  nitrogen,  much 
smaller  losses  and  much  better  utilization  of  the  nitrogen,  would 
have  taken  place.  The  excessive  amounts  of  nitrogen  used 
caused  heavy  losses. 

1  Bulletin  106,  Office  Exp.  Sta.,  U.  S.  Dept.  Agr. 


278  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Gains  of  Organic  Matter. — The  soil  gains  organic  matter 
through  residues  of  crops,  weeds,  green  crops,  and  manure.  Crops 
are  divided  into  two  classes  with  reference  to  their  effect  upon 
the  organic  matter  of  the  soil — namely  humus-decreasing  and 
humus-increasing.  Those  crops  which  leave  enough,  or  more 
than  enough  vegetable  matter  in  their  roots  and  stubble  to  restore 
the  loss  which  takes  place  during  their  growth,  are  called  humus- 
increasing  crops.  They  are  generally  crops  which  receive  little  or 
no  cultivation,  and  which  leave  large  amounts  of  roots  and 
stubble.  Crops  such  as  clover  and  grasses  are  humus-increasing. 

Those  crops  which  do  not  leave  enough  organic  matter  to  re- 
place the  loss  by  oxidation  during  their  growth  are  called  humus- 
decreasing.  On  account  of  the  cultivation  which  these  crops 
receive,  there  is  a  greater  loss  of  organic  matter  than  with  the 
first  group  mentioned,  and  less  organic  matter  is  contained  in  the 
stubble.  Cotton,  corn,  potatoes,  and  beets  belong  to  this  group. 

There  are  some  crops  which  belong  to  the  one  or  the  other  of 
these  groups  according  to  the  disposition  made  of  the  residues 
therefrom.  For  example,  if  rice  straw  is  removed  or  burned,  it 
is  a  humus-consuming  crop,  while  if  the  straw  is  plowed  under 
there  may  be  little  or  no  loss  of  humus. 

The  quantity  of  organic  matter  lost  when  humus-consuming 
crops  are  grown  also  depends  upon  the  disposition  of  the  residues. 
Any  treatment  which  results  in  loss  of  organic  matter  that  might 
be  plowed  under,  such  as  burning  off  of  corn  stalks  or  grass,  etc., 
increases  the  loss  of  organic  matter  from  the  soil,  and  vice  versa. 

Green  crops,  when  plowed  under,  increase  the  organic  matter 
of  the  soil.  Their  chief  use  is  to  secure  nitrogen  from  the  air. 
Plowed  under  very  green,  they  decompose  rapidly  and  may  sour 
the  soil.  If  allowed  to  mature,  decomposition  takes  place  much 
more  slowly.  Manure  is  one  of  the  best  means  of  maintaining 
the  organic  matter  of  the  soil,  but  many  farms  do  not  make 
enough  manure  to  suffice  for  this  purpose. 

Formation  of  Humus. — The  accumulation  of  humus  takes  place 
more  largely  under  conditions  of  reduction  than  conditions  of 
oxidation.  Climate,  weather,  nature  of  soil,  etc.,  are  all  of  in- 


LOSSES  AND  GAINS  BY  THE  SOIL 


279 


fluence.  A  high  temperature  is  favorable  to  decay  only  when 
accompanied  by  sufficient  moisture,  but,  as  a  general  rule,  a  low 
temperature  is  favorable  to  accumulation  of  humus.  The  less 
the  permeability  of  the  soil,  the  slower  is  the  oxidation  and  the 
greater  is  the  accumulation  of  humus.  The  greater  the  quantity  of 
plant  substance  produced,  the  larger  the  accumulation  of  organic 
matter  in  the  soil.  Dry  plant  residues  decay  more  slowly  than 
green,  the  straws  of  cereals  more  rapidly  than  the  leaves  of  trees. 
Wood  decays  more  slowly  than  any  of  the  other  materials  named. 
In  cultivated  soil,  in  spite  of  the  addition  of  manure,  the 
accumulation  of  humus  is  less  than  in  similar  uncultivated  soils 
covered  with  perennial  crops,  such  as  pastures,  forests,  etc.  Both 
lose  organic  matter,  but  the  protective  covering  of  the  latter  de- 
creases the  loss  or  even  causes  an  increase.  The  following  table 
shows  the  carbon  content  of  the  soil  under  three  forms  of  treat- 
ment : 

GRAMS.  OF  CARBON  PER  1,000  GRAMS.  SOIL. 


Corn 

Potatoes 
and  barley 

Sanfoin 

At  the  beginning  

J5-2 
7.6 

7-6 

16.2 

7-i 

9-i 

I2.9 
13-3 

0.4 

Gain  •                •        •  •          ... 

A  loss  of  over  half  the  organic  carbon  in  the  soil  occurred  with 
the  cultivated  crops,  while  with  the  uncultivated  crop  (sanfoin) 
there  was  a  slight  gain.  Manure  was  added  to  the  cultivated  plots. 

It  appears  that  cultivated  soils  become  poorer  in  carbon,  no 
matter  how  much  manure  is  applied,  and  this  impoverishment 
ceases  and  the  soil  begins  to  get  richer  when  the  land  is  filled 
with  perennial  plants. 


CHAPTER  XIV. 


MANURE. 

Manure  consists  of  the  excrements  of  domestic  animals,  mixed 
with  more  or  less  bedding  or  litter.  Barn-yard  manure  is  the 
ordinary  mixture  of  animal  excrements,  litter,  etc.,  which  are 
accumulated  on  the  farm. 

Composition  of  Manure. — Manure  is  very  variable  in  composi- 
tion, depending  on  the  kind  and  age  of  the  animal,  the  kind  and 
amount  of  food,  the  litter  or  absorbents  used,  and  the  method  of 
keeping  or  preserving  it.  Ordinary  barn-yard  manure  which  has 
received  reasonable  care,  may  be  safely  assumed  to  vary  in 
composition  between  the  following  limits: 


Per  cent. 

Average 
per  cent. 

o  4-0  8 

O47 

Phosphoric  Ecid.  

O  2-O  ^ 

T>ntactl 

^•66 

"\X7otpr 

0.49 
67  f> 

The  average  composition  of  carefully  preserved  manure  from 
different  animals  is  about  as  follows  :x 

PERCENTAGE  COMPOSITION  OF  MANURE. 


Water 

Nitrogen 

Phosphoric 
acid 

Potash 

Sheep  

CQ    C 

O  77 

Calves  

oyo 

77  7 

u.// 

Or/-) 

u-oV 
o  1  7 

u-oV 

TTop-c 

OS/i 

**•*  / 

uOv3 

Oow<; 

Jtl-L 

•39 

•33 

/O'O 
/l8  7 

u-4o 

n  /i8 

Hens     

4°'/ 

U'4V 

Comparative  Value  of  Solid  and  Liquid  Manure. — The   solid 

manure  of  animals  consists  of  the  undigested  residues  of  the  food. 

The   urine  contains   the   fertility   ingredients   which   have  been 

digested.     The  composition  of  the  solid  and  liquid   excrement 

1  Beal,  Farmers  Bulletin  No.  77. 


MANURE 


281 


from   farm   animals   is   approximately   as   follows,   though   con- 
siderable variations  occur : 

PERCENTAGE  COMPOSITION  OF  EXCREMENTS. 


Water 

Nitrogen 

Phosphoric 
acid 

Potash 

Solid 

Liquid 

Solid 

Liquid 

Solid 

Liquid 

Solid 

Liquid 

76 

84 
80 
58 

89.0 
92.O 
97-5 

86.5 

0-5 
0-3 
0.6 
0.8 

1.2 

0.8 

0.3 

1.4 

0.4 
0-3 
0-5 
0.6 

trace 
trace 

0.13 
o  05 

0.4 
O.I 

0.4 
0.45 

1-3 

1-3 
0-45 

2.O 

Sheep  •                 

Poultry  excrement,  when  fresh,  contains  about  I  per  cent, 
nitrogen,  0.8  per  cent,  phosphoric  acid,  and  0.4  per  cent,  potash. 
The  results  of  an  experiment  made  at  the  Pennsylvania  Experi- 
ment Station,  to  ascertain  the  distribution  of  the  fertilizing  in- 
gredients among  the  solid  manure,  the  liquid  manure,  and  the 
milk  or  increase  in  weight,  are  as  follows : 


Liquid 
manure 

Solid 
manure 

Milk 
or  increase 

Per  cent. 

CQ 

Per  cent. 

Per  cent. 

1  7 

Phosphoric  acid.  

0U 

oo 

7c 

1  / 
or 

Potash    

IJC 

/O 

16 

•O 

/O 

Loss  of  urine  therefore  involves  the  loss  of  50  per  cent,  of  the 
nitrogen  fed,  and  about  75  per  cent,  of  the  potash. 

Influence  of  Age  and  Kind  of  Animal. — An  animal  which  is 
not  gaining  flesh,  producing  milk,  or  laying  eggs,  etc.,  will  excrete 
practically  all  the  potash,  phosphoric  acid,  and  nitrogen  eaten. 
These  ingredients  are  taken  in  with  the  food,  used,  and  are  ex- 
creted in  the  waste  products.  If  no  flesh,  etc.,  is  produced,  the 
outgo  and  income  must  be  equal.  A  young  growing  animal  retains 
in  the  bones,  flesh,  etc.,  a  portion  of  the  fertilizing  materials  fed  to 
it.  Animals  producing  milk,  laying  eggs,  etc.,  utilize  some  of  the 
phosphoric  acid,  and  nitrogen  in  these  products. 
19 


282  PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

The  Mississippi  Experiment  Station  determined  income  and 
outgo  of  plant  food,  and  found  that  young  fattening  steers  excrete 
on  an  average  84  per  cent,  of  the  nitrogen,  92  per  cent,  of  the 
potash,  and  86  per  cent,  of  the  phosphoric  acid  of  the  food  con- 
sumed. 

Differences  in  the  composition  of  manure  from  differ- 
ent animals  are  due  in  part  to  difference  in  the  food  eaten  by  the 
animal,  and  in  part  to  the  water-content  of  the  manure.  Animals, 
such  as  hogs,  which  feed  on  concentrated  foods,  produce  a 
stronger  manure  than  those  which  require  more  bulky  food,  such 
as  horses  and  cows. 

Sheep  manure  is  a  rich  manure  containing  only  a  small  amount 
of  water.  It  ferments  more  rapidly  than  cow  manure,  but  not 
as  readily  as  horse  manure.  It  is  concentrated  and  valuable  for 
gardening  purposes. 

Horse  manure  is  dry,  undergoes  fermentation  rapidly,  and  gen- 
erates a  high  heat  on  account  of  its  loose  texture.  In  the  pro- 
cess of  fermentation  the  nitrogen  is  converted  into  ammonium 
carbonate,  which,  being  volatile,  is  liable  to  be  lost.  A  well  fed 
horse  at  ordinary  hard  work  will  produce  about  50  pounds  of 
solid  and  liquid  excrement  per  day. 

Hog  manure  is  very  variable  in  composition.  It  contains  much 
water,  ferments  slowly,  and  generates  little  heat  in  fermentation. 

Coiv  manure  is  poorer  than  hog  manure,  decomposes  slowly 
and  generates  little  heat.  A  milch  cow  will  excrete  daily  about  20 
to  30  pounds  liquid  and  40  to  50  pounds  solid  excrement  per  day. 

Poultry  manure  is  rich  in  nitrogen.  It  ferments  rapidly  and 
easily  loses  nitrogen.  In  order  to  prevent  loss  from  volatilization 
as  ammonia,  some  preservative  should  be  added  to  it. 

Quality  and  Quantity  of  Feed. — Since  manure  can  contain  only 
the  fertilizing  constituents  of  the  food,  the  composition  of 
manure  depends  largely  on  the  composition  and  amount  of  the 
food.  If  the  food  is  poor  in  nitrogen,  phosphoric  acid,  and 
potash,  the  manure  will  also  be  poor.  The  richest  manure  will 
be  obtained  when  concentrated  materials  rich  in  nitrogen  are  fed, 
such  as  cottonseed  meal,  gluten  meal,  bran,  clover  hay,  etc.  Since 


MANURE: 


animals  fed  on  heavy  rations  for  fattening  or  for  the  production 
of  milk  must  be  fed  concentrated  food,  it  follows  that  manure  is 
more  valuable  from  these  animals  than  from  animals  fed  for 
maintenance.  In  many  instances  the  value  of  the  fertilizing 
materials  contained  in  purchased  feed  is  nearly  as  great  as  the 
food  value.  This  is  very  often  the  case  with  cotton  seed  meal 
purchased  in  the  Southern  States.  The  farmer  who  saves  both 
solid  and  liquid  excrement  in  the  manure,  is  getting  two  values  for 
the  money  expended.  If  the  liquid  excrement  is  lost,  something 
over  50  per  cent,  of  the  fertilizing  value  of  the  feed  goes  with  it. 
The  fertilizer  constituents  of  the  liquid  manure  are  also  more 
valuable,  pound  for  pound,  than  those  in  the  solid  manure.  The 
liquid  manure  contains  in  solution  and  readily  available  those 
substances  which  have  been  digested  by  the  animal.  The  pur- 
chase of  feeding  stuffs  accompanied  by  the  careful  saving  of 
manure,  is  one  way  to  secure  plant  food  for  the  farm.  This 
method  is  extensively  applied  in  European  countries. 

Different  feeding  stuffs  vary  considerably  in  their  content  of 
plant  food.  The  following  table  gives  the  manurial  value  of 
some  farm  products. 

MANURIAL  VALUE  OF  FARM  PRODUCTS,  POUNDS  PER  TON. 


Nitrogen 

Phosphoric 
acid 

Potash 

8, 

l{\    A 

if>    f\ 

30.0 

.u 

Ar\   2 

•* 

II.4 
08    f\ 

TQC  7 

tA    Q 

1UO-  / 
T  7  c    7 

o*--* 

eft  2 

\yheat  

M>  / 

1*]    r 

Ou-^ 
jr    ft 

29.2 

Oats  

6/-5 
•?5  A. 

1^.0 
T  2  A 

Q   Q 

Porn 

T  T     8 

Rarlpv 

66'  l 

7-4 

Milk 

oV-  / 

io-4 

9.0 

Cheese                                   •    •  • 

QO  6 

•4 

3-° 

yu.u 
C7   2 

23.0 

5-° 

JJ-* 

Ol"i 

3-° 

Kind  and  Amount  of  Litter. — Litter  is  used  to  furnish  a  clean 
bed  for  the  animal  and  to  absorb  the  liquid  excrement.  It  makes 
the  manure  easier  to  handle,  increases  its  physical  (and  in  some 


284 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


cases,  its  chemical)  action  on  the  soil,  and  checks  and  controls 
decomposition.  The  materials  used  for  litter  are  not,  as  a  rule, 
rich  in  fertilizing  ingredients.  It  is  more  important  that  all  the 
fertilizing  ingredients  of  the  manure  should  be  preserved  than 
that  its  percentage  composition  should  be  increased  or  diminished. 

Straw  is  usually  used  for  litter  because  it  is  one  of  the  by- 
products of  the  farm.  It  is  a  good  absorbent,  though  rather  poor 
in  fertilizing  constituents. 

Leaves  are  good  absorbents. 

Dry  peat  is  an  excellent  material,  as  it  has  a  high  absorbing 
power  and  contains  fair  amounts  of  nitrogen. 

Sawdust  is  a  good  absorbing  material,  but  poor  in  fertilizing 
constituents. 

The  composition  of  some  materials  used  as  litter  is  as  follows  :x 
POUNDS  PER  TON  OF  LITTER. 


Nitrogen 

Phosphoric 
acid 

Potash 

l6 

6 

6 

Straw   

8-12 

A  6 

1  2    12 

16 

*«    d* 

Sa  wflimt 

5 

Peat                                     

Losses  of  Manure. — All  the  plant  food  in  the  excreta  of  animals 
cannot  be  saved.  There  are  some  unavoidable  losses  in  nearly  all 
methods  of  collecting  manure.  The  least  loss  of  fertility  occurs 
when  the  animals  are  fed  in  the  field  to  be  manured,  as  the 
excreta,  solid  and  liquid — particularly  the  liquids — are  then 
absorbed  by  the  soil.  When  manure  is  stored  or  preserved,  there 
is  always  a  loss  of  plant  food.  The  Rothamsted  Experiment 
Station  estimates  that,  as  a  rule,  under  English  conditions,  one- 
half  of  the  nitrogen  of  the  feed  is  lost,  one-fourth  of  the  phos- 
phoric acid,  and  none  of  the  potash.  The  chief  causes  of  loss  are 

(1)  seepage,  or  penetration  of  the  liquid  manure  into  the  soil; 

(2)  weathering,  or  exposure  to  rain;  (3)  fermentation. 
1  Beal,  Farmers  Bulletin  No.  77. 


MANURE:  285 

When  the  animals  are  stabled  on  a  wood  or  dirt  floor  with  in- 
sufficient bedding,  a  portion  of  the  liquid  excrement  soaks  into 
the  ground.  The  quantity  depends  upon  the  tightness  of  the  floor 
and  the  absorptive  power  of  the  manure  or  the  litter.  A  similar 
loss  occurs  when  the  manure  is  stored  in  piles  on  the  earth.  A 
portion  of  the  liquids  sink  in  the  earth.  Cement  floors  prevent 
such  losses,  and  are  used  to  a  considerable  extent  in  certain 
localities.  Clay  when  worked  until  puddled,  and  then  tamped, 
makes  a  fairly  good  floor. 

Loss  by  seepage  may  be  decreased  by  using  the  proper  quantity 
of  litter,  and  by  collecting  and  preserving  the  manure  on  an  im- 
pervious floor.  An  excess  of  litter  makes  the  manure  too  coarse. 
The  following  table1  shows  the  absorptive  power  of  various 
litters : 

Water  retained  by 

100  pounds  material 

after  24  hours 

Wheat  straw 220 

Oak  leaves  (partly  decomposed) 162 

Sawdust    435 

Peat  600 

Peat  moss 1,300 

Soil  rich  in  humus  .    50 

The  amount  of  litter  should  depend  on  the  character  of  the 
food.  Watery  foods  and  those  containing  much  nitrogen  increase 
the  secretion  of  urine  and  so  increase  the  amount  of  litter  neces- 
sary to  absorb  the  urine  and  keep  the  animal  clean.  Manure  pro- 
tected from  rain  by  a  shed,  according  to  Kinnard,  produced  4 
tons  more  per  acre  of  potatoes,  and  n  bushels  more  wheat,  than 
the  same  quantity  of  manure  not  protected  by  a  shed  during  the 
same  period  of  time. 

When  manure  is  exposed  to  rain,  a  part  of  the  fertilizing  con- 
stituents is  washed  away,  somewhat  in  proportion  to  the  length 
of  the  exposure  and  the  amount  of  rain.  The  soluble  ingredients 
so  lost  are  the  more  available  and  more  valuable  part  of  the 
manure.  Experiments  have  been  made  in  which  a  quantity  of 
manure  was  weighed  and  subjected  to  analysis  and  after  a  certain 
1  Herbert,  Exp.  Sta.  Record  No.  5,  p.  144. 


286 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


period,  again  weighed  and  analyzed.     The  following  are  some  of 
the  results : 


Where  made 

New  York 

New 

Jersey* 

New 

Jersey1 

Canada 

Ohio? 

Material 

Hon-e 
manure 

Cow  dung 

Dung 
and  urine 

Horse 
manure 

Steer 
manure 

1  80 
5<># 

50  fo 
50  % 

109.0 
37-6 

51-9 

47.1 

109 
51 
51 
61 

365 
33 
16 

34 

90 
28 
H 
58 

L/oss  of  nitrogen  per  cent  .  . 

Exposure  to  rain  certainly  involves  a  considerable  loss  of 
fertility. 

Fermentation.3 — Two  classes  of  bacteria  take  part  in  the  fer- 
mentation of  manure  ( I )  Aerobic,  which  live  only  in  the  presence 
of  oxygen,  (2)  Anaerobic,  which  live  only  when  oxygen  is  ex- 
cluded. On  the  outer  surface  of  the  heap,  the  aerobic  bacteria 
are  active,  while  the  anaerobic  ferments  act  in  the  interior  of  the 
heap  where  the  supply  of  air  is  limited.  The  anaerobic  bacteria 
are  less  vigorous  in  their  action  than  the  aerobic.  They  often 
produce  foul  smelling  gases.  The  fermentation  also  varies  ac- 
cording to  circumstances.  It  depends  on  the  temperature,  the 
supply  of  air,  the  moisture,  the  composition  of  the  material,  and 
the  preservatives  used. 

The  optimum  temperature  for  manure  fermentation  is  about 
131°  F.  The  temperature  may  rise  high  enough  to  set  the  mass 
on  fire,  if  it  is  dry  enough.  The  temperature  of  the  interior  of 
the  heap,  where  anaerobic  fermentation  is  in  progress,  rarely 
rises  over  95°  F. 

The  supply  of  air  is  determined  by*  the  compactness  of  the  heap. 

1  Bulletin  150. 

2  Bulletin  183. 

3  Herbert,  Exp.  Sta.  Record  5,  p.  146. 


MANURE  287 

If  the  heap  is  too  loosely  built,  the  fermentation  is  too  rapid,  and 
large  losses  of  nitrogen  will  occur. 

Moisture,  by  lowering  the  temperature  and  excluding  air,  re- 
tards fermentation ;  loss  of  manure  is  decreased  by  keeping  the 
manure  properly  moistened.  Alternate  wetting  and  drying  is 
also  bad. 

Manure  decreases  rapidly  in  bulk  during  fermentation,  the 
substances  of  which  it  is  composed  being  decomposed  partly  into 
carbon  dioxide  and  water.  When  the  fermentation  is  not 
properly  controlled,  nitrogen  may  escape  as  free  gas  or  as  am- 
monia. The  coarse  materials  are  gradually  decomposed  and  are 
to  a  considerable  extent  dissolved  in  the  black  liquid  which  oozes 
out  of  the  manure  heap.  The  mineral  matter  is  also  rendered 
more  soluble. 

The  nitrogen  in  the  liquid  excrement  is  mostly  present  as  urea 
or  hippuric  acid.  These  undergo  fermentation  rapidly,  especially 
in  a  warm  climate,  producing  ammonium  carbonate,  and  con- 
siderable amounts  of  ammonia  may  escape  into  the  air.  Ammonia 
is  produced  in  fermenting  manure,  and  if  the  manure  is 
allowed  to  dry  out,  or  is  too  freely  exposed  to  the  air,  consider- 
able losses  of  ammonia  take  place. 

Fermentation  is  controlled  by  keeping  the  manure  heap  com- 
pact and  moist,  and  by  the  use  of  preservatives.  Sprinkling  the 
mass  with  water  or  liquid  manure  excludes  air  and  prevents  loss 
of  ammonia.  If  the  mass  dries  out,  nitrogen  is  lost.  Gypsum 
(land  plaster),  kainit,  and  acid  phosphate  are  preservatives  re- 
commended to  prevent  loss  of  manure  during  fermentation,  but 
it  is  doubtful  whether  they  have  any  appreciable  effect. 

Methods  of  Saving  Manure. — The  following  are  some  methods 
of  saving  manure: 

(i)  Grlgnon  Method. — This  method  is  used  extensively  in 
France.  The  manure  is  piled  upon  a  stone  or  cement  pavement 
in  the  farm  courtyard,  in  flat,  well  packed  layers.  The  liquid 
manure,  and  the  drainage  from  the  manure  pile  runs  into  a  stone 
cistern.  From  time  to  time  the  liquid  manure  is  pumped  over  the 
pile  of  solids.  The  object  of  this  is  to  keep  the  manure  moist 


288 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


and  to  prevent  loss  by  excessive  fermentation,  and  also  to  cause 
the  manure  to  decompose  evenly.     When  thoroughly  rotted,  the 


Fig.  68.— The  Grignon  system  of  keeping  manure. 


Fig.  69. — Liquid  manure  spreader.     Switzerland. 

manure  is  very  dark,  brittle  mass,  and  is  said  to  be  very  effective 
in  its  action. 


MANURE  289 

(2)  Liquid  Manure  Method. — This  method  is  used  in  Ger- 
many, Belgium,  and  Holland.  The  liquid  manure  is  carried  to  an 
underground  tank  by  means  of  stone  troughs.     The  solids  are 
kept  separate.     The  liquid  manure  is  pumped  out  and  applied  to 
the  soil  about  six  times  a  year,  or  oftener. 

(3)  Deep-Stall  Method. — The  animals  are  kept  in  deep  stalls 
with  paved  floors.     Sufficient  bedding  is  used  to  keep  the  animal 
dry  and  the  manure  is  allowed  to  accumulate  in  the  stall.     The 
feeding  rack  and  water  vessels  are  hung  on  chains,  so  that  they 
can  be  raised  as  the  manure  accumulates.     The  manure  is  taken 
out  once  or  twice  a  year.     When  the  climate  is  cool,  this  method 
has  given  good  results.     At  the  Pennsylvania  Station,1  there  was 
a  loss  of  only  5.7  per  cent,  of  the  nitrogen,  5.6  per  cent,  potash, 
and  8.5  per  cent,  potash,  compared  with  34.1  per  cent,  nitrogen, 
19.9  per  cent,  potash,  and  14.2  potash  lost  from  similar  manure 
in  a  covered  shed. 

(4)  Absorption  Method. — The  liquids  are  absorbed  with  straw, 
peat,  sawdust,  or  dirt,  etc.,  and  taken  out  with  the  solids.     The 
manure  is  allowed  to  accumulate,  or  hauled  out  to  the  fields  daily. 

(  5 )  Feeding  Off  and  Pasturing. — When  the  crops  are  pastured 
or  fed  off,  the  manure  is  dropped  directly  in  the  field. 

Application  of  Manure. — The  kind  and  amount  of  manure  to 
be  applied  depends  on  conditions.  The  least  loss  takes  place  when 
the  manure  is  applied  as  fresh  as  possible.  Manure  decays  more 
rapidly  in  an  open  soil  than  in  a  close  soil  (clay).  If  it  is  desired 
to  improve  the  mechanical  condition  of  a  clay,  fresh  manure  should 
be  applied,  but  the  fertilizing  constituents  act  more  rapidly  in  a 
clay  soil  when  manure  is  well  rotted.  Fermenting  manure  seri- 
ously injures  the  quality  of  tobacco,  sugar  beets,  and  potatoes. 

The  manure  may  be  (a)  placed  in  heaps,  and  then  spread,  (b) 
spread  broadcast  and  ploughed  in,  (c)  applied  in  hill  or  drill  with 
seed.  The  first  method  is  objectionable,  as  the  small  heaps  may 
lose  fertility  rapidly,  and  the  spots  made  much  richer  than  the 
remainder  of  the  field.  The  second  method  is  good  if  the  manure 
1  Bulletin  63. 


2QO  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

is  soon  ploughed  in.  The  third  method  is  applicable  to  some 
truck  crops. 

The  amount  of  manure  applied  varies  from  3  to  40  tons  per 
acre.  In  arid  JOT  dry  climates,  the  manure  should  be  composted, 
and  well  rotted.  Coarse  manure  should  not  be  plowed  under  in 
the  spring  in  dry  sections,  as  the  layer  of  manure  will  break  the 
connection  between  plowed  and  unplowed  soil,  and  cause  the 
plowed  soil  to  dry  out  more  rapidly,  thereby  losing  water  needed 
for  the  crops.  Coarse  manure  may  be  applied  best  as  a  top  dress- 
ing on  pasture  land. 

Well  rotted  manure  may  cause  wheat  to  lodge.  It  can  be 
applied  to  corn. 

Practice  in  applying  manure  varies.  In  some  places,  heavy 
applications  are  made  every  four  years  or  more.  In  other  places, 
it  is  applied  annually  in  smaller  quantities.  It  is  probably  better 
to  apply  the  manure  once  in  a  rotation  of  crops  to  the  crop  which 
does  best  with  it.  Manure  is  valuable  not  only  for  the  plant  food 
which  it  contains,  but  also  for  its  physical  and  chemical  effects  on 
the  soil.  The  lasting  effects  of  manure  are  shown  by  experi- 
ments at  Rothamsted  and  Woburn,  England.  At  Rothamsted, 
one  plot  had  received  manure  for  20  years,  and  none  after  that. 
Barley  has  been  grown  on  this  plot  for  58  years,  and  still  shows 
the  effect  of  the  manure  applied  38  years  ago.  Thirty  years 
after  the  last  application  of  the  manure,  the  crop  of  barley  on  the 
manured  plot  was  twice  as  large  as  that  which  had  never  received 
any  fertilizer  or  manure.  At  Woburn  a  plot  which  had  received 
manure  a  few  years  continued  for  25  years  to  give  better  yields 
than  one  which  had  received  no  manure. 

Green  Manures  and  Cover  Crops.1 — Green  manures  and  cover 
crops  are  planted  to  be  plowed  under.  It  is  of  course  more  de- 
sirable to  feed  the  crop  and  save  the  manure,  thereby  utilizing  its 
feeding  value  and  most  of  its  fertilizing  value,  but  this  procedure 
is  not  always  practicable. 

The  objects  of  green  manure  and  cover  crops  are  as  follows : 

(i)  To  supply  organic  matter  to  the  soil. 
1  Farmers  Bulletin  278. 


MANURE: 


291 


(2)  To  prevent  loss  of  plant  food  by  leaching.     The  soil  is 
covered  with  a  crop  instead  of  being  left  bare.     The  crop  takes 
up  most  of  the  plant  food  in  solution  and  prevents  it  being  washed 
out  of  the  soil. 

(3)  To  secure  nitrogen  from  the  air  for  the  use  of  succeeding 
crops.     For  this  purpose,  leguminous  crops  should  be  grown,  and 
they  must  be  infected  with  the  proper  organism. 

Green  manures  should,  if  possible,  be  allowed  to  mature  before 
being  plowed  under.  A  large  mass  of  easily  decaying  matter 
may  sour  the  soil  and  injure  it  for  some  years.  Lands  which  are 
decidedly  wet  are  also  not  benefited  by  green  manures,  as  they 
may  denitrify.  An  acid  condition  of  the  soil  may  be  corrected  by 
lime. 

As  a  rule,  it  is  best  to  follow  green  manures  with  cultivated 
crops.  The  tillage  of  such  crops  hastens  the  decay  of  the 
vegetable  matter,  and  by  aerating  the  soil,  favors  additional  nitro- 
gen fixation  by  the  soil  bacteria.  Corn,  cotton,  potatoes,  and 
heavy  tobacco  derive  great  benefit  from  green  manures. 

The  following  table  shows  the  effects  of  green  manures  on 
crops  compared  with  crops  on  the  same  soil  which  had  no  green 
manure. 


Locality 

Manure  crop 

No  manure 

Green  manure 

Illinois  •  • 
Ottawa  •  . 

red  clover 

35.7  (grown  continuously) 
^8  8  (  T  vear^i 

55.1  bu.  corn 

Ottawa  •  . 

2Q  o   .          .... 

Arkansas 
Alabama  • 

cowpeas 
cowpea  vines 

10.1  (continuous  4  years)  • 

877  o   •  . 

14.1  bu.  wheat 

Alabama  • 

cowpea  vines 

12  A.  bushels  

22  8  bu   oats 

Maryland 

crimson  clover 

C2  8  bushels  

Maryland. 

crimson  clover 

67  8  bushels  

Fallen  leaves  and  stubble  have  some  fertilizing  value,  even 
when  the  crop  is  cut  for  hay.  For  example,  at  the  Alabama  Ex- 
periment Station,  36.6  of  the  entire  weight  of  the  cowpea  plant 
was  found  to  be  in  the  fallen  leaves  and  stubble.  The  hay  in  one 
experiment  contained  55.8  pounds  nitrogen  per  acre,  the  fallen 
leaves  and  stubble  31.4  pounds. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Effects  of  Manure. — Some  effects  of  manures  are  as  follows: 
(i)  They  make  clay  soils  more  porous,  in  better  tilth  and  more 
easily  worked.  (2)  They  make  sandy  soils  more  retentive  of 
moisture.  (3)  They  improve  the  physical  character  of  the  soil 
and  make  it  better  suited  for  plant  growth.  (4)  They  supply 
nitrogen  and  other  plant  food.  (5)  They  supply  organic  matter 
which  may  aid  soil  bacteria  to  fix  free  nitrogen.  (6)  They  are 
lasting  in  their  effects. 


CHAPTER  XV. 


SOURCES  AND  COMPOSITION  OF  FERTILIZERS. 

When  knowledge  that  certain  elements  are  essential  to  plant 
life  was  first  secured,  the  action  of  various  elements  were  tested 
in  practice  upon  soils  in  order  to  see  which  of  these  are  not  pres- 
ent in  sufficient  quantity.  For  example,  at  Rothamsted,  plots  are 
still  fertilized  with  sulphate  of  magnesia.  In  the  process  of  time, 
it  was  found  that  phosphoric  acid,  potash,  and  nitrogen  were  the 
substances  needed  for  plant  food,  and  a  fertilizer  is  now  generally 
defined  as  a  substance  which  contains  phosphoric  acid,  potash,  or 
nitrogen,  or  a  mixture  of  them,  and  is  used  as  an  application  to 
the  soil  to  promote  the  growth  of  plants.  A  further  requirement 
is  that  the  potash,  phosphoric  acid,  or  nitrogen  be  in  such  forms 
as  to  be  readily  taken  up  by  plants.  The  value  of  the  fertilizer 
is  based  upon  the  amount  of  these  three  substances  it  contains. 

Fertilizers  have  other  effects  on  the  soil  in  addition  to  their 
supply  of  plant  food.  They  may  affect  its  acidity  or  alkalinity, 
its  physical  structure,  etc.  Substances  which  contain  little  or 
no  phosphoric  acid,  potash,  or  nitrogen,  and  are  used  upon  the 
soil  for  other  reasons,  are  termed  amendments.  Lime,  for 
example,  is  an  amendment. 

Nitrogenous  Fertilizers. — Nitrogenous  fertilizers  are  divided 
into  two  groups,  inorganic  and  organic.  The  two  inorganic 
materials,  nitrate  of  soda  and  ammonium  sulphate,  may  be  directly 
assimilated  by  plants,  though  the  ammonium  sulphate  usually 
undergoes  some  nitrification  and  is  converted  partly  into  nitrates. 
Organic  substances,  such  as  dried  blood,  cottonseed  meal,  tank- 
age, etc.,  must  first  undergo  changes  in  the  soil,  by  which  the 
nitrogen  is  converted  into  ammonia  or  into  nitrates,  or  into 
organic  compounds  which  can  be  assimilated  by  plants.  The  dif- 
ferent nitrogenous  fertilizers  have  different  agricultural  values, 
depending  on  the  readiness  with  which  they  can  be  assimilated. 

Inorganic  Nitrogenous  Materials. — Nitrate  of  soda  is  found  in 
the  rainless  districts  of  South  America  mixed  with  dirt  and  com- 
mon salt,  as  deposits  termed  caliche.  It  contains  on  an  average 


294 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


about  25  per  cent,  nitrate  of  soda.  The  best  quality  of  caliche  con- 
tains approximately  50  per  cent,  nitrate  of  soda,  NaNO3,  26  per 
cent,  common  salt,  6  per  cent,  sulphate  of  soda,  14  per  cent,  dirt, 
etc.,  insoluble  in  water,  and  about  4  per  cent,  magnesium  sulphate 
and  chloride,  with  small  amounts  of  sodium  iodide.  The  caliche 
is  treated  with  hot  water  and  the  solution  run  into  crystallizing 
vats.  The  crude  nitrate  of  soda  crystallizes  out  on  cooling. 
Nitrate  of  soda  is  readily  soluble  in  water,  easily  taken  up  by 


Fig.  70.  —Nitrate  of  soda,  partly  blasted  up. 

plants,  and,  unless  taken  up  by  plants,  will  be  washed  from  the 
soil.  It  contains  about  15  per  cent,  of  nitrogen.  It  is  often 
called  chile  saltpeter. 

Sulphate  of  ammonia  is  a  by-product  obtained  in  the  manu- 
facture from  coal,  of  illuminating  gas,  and  of  coke.  A  part  of  the 
nitrogen  of  the  coal  passes  off  as  ammonia,  and  is  removed  by 
passing  the  gas  through  sulphuric  acid,  forming  sulphate  of  am- 
monia (NH4)2SO4.  It  contains  about  20  per  cent,  of  nitrogen. 
Ammonia  is  fixed  by  the  soil,  and  is  not  as  available  to  plants  a$ 


SOURCES  AND   COMPOSITION   OF   FERTILIZERS 


295 


nitrates,  or  as  easily  washed  out.  It  changes  to  nitric  acid  in  the 
soil,  and  nitric  acid  and  sulphuric  acid  unite  with  lime  to  form 
nitrates  and  sulphates.  The  use  of  ammonium  sulphate  tends  to 
decrease  the  carbonate  of  lime  in  the  soil,  or  to  render  the  soil 
acid. 

Calcium  Cyanamide. — This   substance  is  prepared  by  passing 
atmospheric  nitrogen  over  calcium  carbide.    It  decomposes  slowly 


Fig.  71. — Crystallizing  pans  with  nitrate  of  soda. 

in  the  soil,  with  the  production  of  nitrates.  Under  the  most 
favorable  conditions,  it  appears  to  have  a  value  equal  to  sodium 
nitrate,  but  if  applied  too  soon  before  planting,  or  to  acid  humus 
soils,  it  may  have  injurious  effects. 

Organic  Materials. — The  organic  nitrogenous  fertilizers  cannot 
be  taken  up  directly  by  plants  but  must  first  be  converted  into  am- 
monia or  nitrates.  Their  value  depends  upon  their  content  of 
nitrogen,  and  the  readiness  with  which  they  undergo  decomposi- 
tion in  the  soil. 


296  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Dried  blood  comes  from  the  large  slaughtering  establishments, 
and  is  of  two  kinds,  red  and  black.  The  red  dried  blood  results 
from  drying  at  the  temperature  of  boiling  water,  at  which  tem- 
perature it  does  not  char.  The  black  dried  blood  is  dried  at  a 
higher  temperature,  and  decays  more  slowly.  Dried  blood  is  one 
of  the  most  concentrated  organic  nitrogenous  fertilizers.  It  con- 
tains about  ii  per  cent,  nitrogen.  It  decays  quickly  in  the  soil. 

Dried  meat  or  meat  meal  is  obtained  from  rendering  establish- 
ments, where  the  different  portions  of  dead  animals  are  variously 
utilized.  It  is  rich  in  nitrogen,  and,  like  blood,  decays  rapidly.  It 
also  comes  from  slaughter  houses  where  the  waste  meat  is  kept 
separate  from  the  tankage. 

Dried  fish  or  fish  scraps  come  from  two  sources :  first,  the  offal 
of  fish  canneries,  and  second,  the  fish  pomace  resulting  from  the 
extraction  of  oil  from  Menhaden  or  other  fish.  The  latter  pro- 
duct is  more  uniform  than  the  former,  containing  7  to  9  per  cent, 
of  nitrogen  and  6  to  8  per  cent,  phosphoric  acid.  Fish  unfit  for 
eating  may  be  caught,  the  oil  extracted,  and  the  residue  prepared 
into  fish  guano. 

Tankage  consists  chiefly  of  the  dried  animal  wastes  from  the 
large  slaughtering  establishments;  to  some  extent  it  comes  from 
the  garbage  plants  of  large  cities.  It  is  very  variable  in  com- 
position, since  it  contains  all  parts  of  the  carcass  which  cannot  be 
used  for  other  purposes — the  bones,  tendons,  flesh,  etc.  Tankage 
varies  so  much  that  it  is  always  sold  in  the  trade  on  the  basis  of 
its  composition,  and  each  shipment  is  subjected  to  analysis.  It 
contains  5  to  10  per  cent,  nitrogen  and  6  to  15  per  cent,  phosphoric 
acid.  As  a  rule  the  fat  and  gelatine  are  removed  by  treatment 
with  super-heated  steam.  Garbage  tankage  is  less  valuable  than 
slaughter  house  tankage.  It  contains  approximately  3  per  cent, 
nitrogen  and  1.2  per  cent,  each  of  phosphoric  acid  and  potash. 

Cottonseed  meal  is  prepared  by  grinding  the  cake  left  from 
pressing  the  oil  from  cottonseed  kernels.  It  is  one  of  the  best 
vegetable  fertilizers.  It  is  an  excellent  cattle  feed,  and  its  most 
economical  use  takes  advantage  of  both  its  feeding  and  its 
fertilizing  values,  by  feeding  the  meal  and  saving  the  manure.  It 


SOURCES  AND   COMPOSITION   OF   FERTILIZERS  297 

contains  6  to  8  per  cent,  nitrogen,  about  1.5  per  cent,  potash,  and 
2.5  per  cent,  phosphoric  acid. 

Cotton  seed  have  approximately  one-half  the  fertilizing  value  of 
the  meal.  They  contain  approximately  3  per  cent,  nitrogen  and 
1.2  per  cent,  each  of  phosphoric  acid  and  potash. 

Linseed  meal  contains  less  nitrogen  than  cottonseed  meal.  The 
demand  for  this  product  for  feeding  purposes  makes  it  an 
expensive  source  of  nitrogen  in  fertilizers. 

Castor  pomace  is  not  useful  as  a  cattle  food.  It  is  about  as 
rich  as  linseed  meal,  and  is  a  good  fertilizer.  It  contains  5  to  6 
per  cent,  nitrogen  and  i.o  to  1.5  per  cent,  each  of  phosphoric  acid 
and  potash. 

Bat  guano  is  the  excrement  of  bats,  found  to  a  limited  extent 
in  caves  in  Texas,  Mexico,  and  Porto  Rico.  It  is  liable  to 
spontaneous  combustion,  the  residue  being  known  as  bat  guano 
ash,  which  is  not  easily  distinguished  from  bat  guano.  Bat  guano 
is  variable  in  composition,  ranging  from  a  compound  rich  in  nitro- 
gen to  one  rich  in  phosphoric  acid.  It  contains  from  2  to  12  per 
cent,  nitrogen  and  from  i  to  8  per  cent,  phosphoric  acid. 

Hoof  and  horn  meal  is  a  by-product  from  the  making  of  var- 
ious articles  from  hoofs  and  horns.  It  contains  about  14  per 
cent,  nitrogen. 

Slowly  Available  Nitrogenous  Fertilizers. — These  materials  give 
up  their  nitrogen  very  slowly,  so  that  they  often  have  little  or  no 
effect  upon  the  crop  to  which  they  are  applied.  In  many  States 
the  use  of  these  materials  in  mixed  fertilizers  is  prohibited. 

Leather  scraps  is  a  waste  product  from  various  factories,  and 
is  sold  as  raw  leather,  steamed  leather,  and  roasted  leather.  It 
contains  about  7  to  8  per  cent,  nitrogen. 

Hair  is  a  product  from  slaughter  houses,  containing  9  to  14  per 
cent,  nitrogen. 

Peat  and  muck  may  contain  as  much  as  2  per  cent,  nitrogen. 

Wool  waste  is  a  by-product  from  woolen  factories. 

Availability  of  Nitrogenous  Fertilizers. — The  nitrogen  of  nitrate 
of  soda  and  ammonium  sulphate  may  be  taken  up  directly  by 
plants,  but  the  value  of  the  other  nitrogenous  materials  depends 
20 


298  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

upon  the  rapidity  and  extent  with  which  they  become  changed  to 
nitrates  and  ammonia  in  the  soil.  It  is  important  to  know  the 
relative  values  of  these  materials.  The  measure  of  their  value  is 
the  quantity  of  nitrogen  which  may  be  secured  from  them  by 
plants  under  favorable  conditions.  This  is  termed  availability. 

Availability  is  based  upon  value  to  plants  in  pot  experiments. 
For  the  purpose  of  comparing  nitrogenous  materials,  a  soil 
decidedly  deficient  in  nitrogen  is  selected,  mixed  thoroughly,  and 
an  equal  quantity  placed  in  a  number  of  pots.  Each  pot  then 
receives  an  equal  and  abundant  amount  of  phosphoric  acid, 
potash,  and  lime  if  necessary.  One  set  of  pots  (two  or  more)  re- 
ceives no  nitrogen.  The  others  receive  an  equal  quantity  of  nitro- 
gen, say  0.3  gram  for  example,  in  the  form  of  nitrate  of  soda,  sul- 
phate of  ammonia,  cottonseed  meal,  or  other  substances  to  be 
tested.  An  equal  number  of  seeds  of  equal  weight  are  planted  in 
eacn  pot,  and  the  crops  are  grown  under  the  same  conditions  as 
regards  moisture,  air,  light,  etc.  They  are  then  harvested,  and 
the  quantity  of  nitrogen  secured  from  each  pot  determined.  This 
nitrogen  comes  from  both  soil  and  fertilizer.  The  quantity  of 
nitrogen  secured  from  the  pots  to  which  no  fertilizer  nitrogen 
has  been  added  is  subtracted  from  the  others  to  ascertain  how 
much  nitrogen  was  secured  from  the  fertilizer.  The  amount  of 
nitrogen  taken  from  one  of  the  materials  (usually  sodium  nitrate) 
is  adopted  as  a  standard,  (equal  to  100)  and  the  results  expressed 
in  terms  of  this.  For  example,  if  0.250  gram  nitrogen  was  secured 
from  sodium  nitrate  by  the  plants  and  0.180  gram  from  cottonseed 
meal,  the  availability  of  the  nitrogen  of  cottonseed  meal  would 
be  0.250 :  180 : :  100 :  x,  or  equal  to  72. 

Considerable  care  is  required  in  the  conduct  and  planning  of 
experiments  of  this  kind.  Two  or  more  pots  must  be  used  for 
each  material.  Nitrogen  must  be  the  controlling  factor  in  the 
growth  of  the  crop,  and,  in  order  to  be  certain  such  is  the  case,  it 
is  best  to  have  several  sets  of  pots  with  different  amounts  of  nitro- 
gen, such  as  0.3,  0.6,  1.2  grams  per  pot  for  example.  If  nitrogen  is 
the  limiting  condition,  as  it  should  be,  the  amount  of  nitrogen 
taken  up  by  the  plants  will  be  in  proportion  to  the  quantity 


SOURCES  AND  COMPOSITION   OF   FERTILIZERS 


299 


applied.     If   there  are  other   limiting  conditions,   the  series   to 
which  they  apply  should  be  rejected. 

Some  workers  have  taken  the  weight  of  the  crop  as  a  measure 
of  the  availability  of  nitrogen,  but  since  the  object  of  the  work  is 
to  ascertain  what  proportion  of  the  nitrogen  of  the  fertilizer  can 
be  taken  up  under  the  most  favorable  conditions,  it  is  obvious  that 
the  amounts  of  nitrogen  recovered  is  the  only  correct  measure. 
The  nitrogen  taken  up  by  the  crops  is  not  necessarily  in  propor- 
tion to  their  weights.  For  example,  Johnson,  Britton,  and  Jenkins1 
secured  the  following  results,  with  oats : 


Amount  of  nitrogen  applied  grams  .  . 
Ratio  of  nitrogen  

0.8 

IO.O 

31.7 

IO.O 

0.384 

IO.O 

1.6 

2O.O 

57-8 
18.0 
0.778 

20.0 

2.4 
30.0 
27.7 
9.0 
1.064 
28.0 

3-2 
40.0 

40.7   ' 
13.0 
1.404 

36.5 

^^eight  of  crop  granjt>  

In  this  experiment,  the  quantities  of  nitrogen  taken  up  are 
nearly  in  proportion  to  the  amounts  of  nitrogen  applied,  but  the 
weights  of  the  crops  are  not. 

Conditions  which  Affect  Availability. — The  conditions  which 
affect  nitrification  also  affect  availability,  since  nitrification  is 
a  necessary  process  for  the  preparation  of  active  nitrogen.  The 
length  of  the  growing  season  is  an  important  factor ;  a  long  grow- 
ing season  being  relatively  more  favorable  to  the  slowly  nitrified 
materials.  If  a  crop  is  grown  and  harvested  and  then  a  second  crop 
grown  without  any  addition  of  fertilizer  nitrogen,  the  slowly  act- 
ing nitrogen  will  appear  relatively  more  effective  than  if  one  crop 
only  is  considered.  For  example,  Voorhees  found  the  availability 
of  fresh  solid  manure  (compared  with  nitrate  of  soda  equal  to 
100)  to  be  12  when  one  crop  (oats)  alone  was  considered,  but  43 
when  the  nitrogen  in  two  crops,  oats  and  millet,  was  taken. 

On  account  of  the  effect  of  the  conditions  of  the  experiment, 

and  also  on  account  of  the  error  inherent  in  the  method  of  work, 

considerable   differences   in   the   availability   of   the  nitrogen   of 

fertilizers   are   observed  by   different   workers.     The    following 

1  Report  Connecticut  Exp.  Sta.,  1893. 


300 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


table  gives  some  determinations  made  on  some  ordinary  nitro- 
genous materials : 

COMPARATIVE  AVAILABILITY  OF  NITROGEN  FERTILIZERS. 


Connecticut  Station 
4  seasons.     1894-7 

Wagner 
3  years 

Average 

Pfeiffer 
et.  al.,  1895-7 

Average 

Maximum 
and 
minimum 

Average 

Nitrate  of  soda  

100 

60-78 
72-87 
64-70 

57-77 

49-73 
65-81 
69-74 
0.0-1.9 
55-76 
8.1-18.5 
7.1-10.2 

ICO 
69 

68 
17 
67 

66 

70 
i 
65 
13 
9 

100 
69 

64 
61 

63 
67 

20 

54 
33 
68 

32 

100 
87 
85 

85 

66 

46 
56 

Fish 

Barnyard    manure    preserved 

Comparative  Availability. — The  availability  of  nitrogenous  fer- 
tilizers for  different  series  of  experiments  made  by  the  same  in- 
vestigator exhibit  considerable  differences.  Some  workers  have 
studied  only  the  effect  upon  the  first  one  or  two  crops,  while 
others  take  into  consideration  the  effect  on  several  succeeding 
crops.  The  results  of  the  Connecticut  Station1  given  in  the  table, 
were  secured  in  three  series  of  experiments  with  (i)  corn,  (2) 
oats  and  corn,  and  (3)  corn,  in  10  pounds  artificial  soil  composed 
of  coal  ashes  and  3  per  cent,  moss,  the  root  and  fertilizer  residues 
remaining  in  the  soil  from  year  to  year.  A  fourth  series,  with 


1  Connecticut  State  Station  Report,  1897,  p.  257. 


SOURCES  AND  COMPOSITION   OF  FERTILIZERS 


301 


oats  and  Hungarian  grass  was  made  on  25  pounds  sandy  loam. 
The  results  of  Wagner  were  on  small  plots  with  summer  rye,  flax, 
summer  wheat,  and  carrots,  and  are  the  average  of  3  seasons. 
Pfeiffer  and  associates  used  27  kgs.  poor  sandy  soil,  and  the 
effect  of  the  residues  for  two  years  was  considered,  which  in- 
creased the  value  of  stable  manure  decidedly. 

Voorhees  at  the  New  Jersey  Experiment  Station1  made  experi- 
ments with  out-of-door  cylinders,  3  square  feet  surface  area  and 
4  feet  deep,  with  corn,  oats,  and  millet,  oats  and  corn.  Considera- 
tion of  the  second  crop  in  each  case  increased  the  availability  of 
manure  decidedly.  Root  residues  and  fertilizer  residues  probably 
remained  for  succeeding  crops,  unless  washed  out  during  the 
winter.  Some  of  his  results  are  as  follows : 


Oats 

Oats  and 
millet 

Oats 

Average2 

1898-1907 

Ammonium  sulphate  • 

flC\   1 

Dried  blood.  

/**y 

c«  c 

77-9 
fii  i 

yo.  2 

f.Q       A 

09-7 

Fresh  manure   solid  

o°-o 

01  .<, 

O4.4 

Solid  manure   leached  

12  O 

4o-u 

35-9 

3Q      Q 

Solid  and  liquid    fresh  

tr»  o 

88  o 

o.y 

Solid   liquid   leached  

•27    Q 

OO'U 

OO'U 

4o>x 

Biological  Methods  of  Availability. — Since  organic  materials 
must  be  transformed  into  ammonia  and  nitrates  before  being 
taken  up  by  plants,  the  quantity  of  ammonia  and  nitrates  pro- 
duced from  a  given  amount  of  nitrogen  in  the  soil,  with  not  too 
short  a  period,  may  be  used  for  comparing  nitrogenous  materials. 
The  quantity  of  nitrates  produced  from  0.3  gram  nitrogen  in  500 
gram  soil  in  four  weeks  varied  with  different  soils,  and  was  not  in 
proportion  to  the  value  of  the  materials,  but  the  quantity  of  nitro- 
gen converted  into  nitrates  and  ammonia  was  in  proportion  to  the 
availability  of  the  material.  The  following  table  gives  some  of 
the  results. 

1  Report,  1901,  p.  144. 

-  Voorhees  and  Lipman,  Bulletin  221,  New  Jersey  Station. 


302 


PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 


Fertilizer1 

Percentage  of  added  nitrogen  converted  into 

Nitrates 

Nitrate 
and  ammonium 

Soil  No.  75 
8.2 

6.6 
18.6 
17.5 

Soil  No.  77 

20.3 

23-1 
17.6 
17-8 
9.6 

Soil  No.  75 

SI'S 

56.4 
20.7 
29.1 

Soil  No.  77 

394 
43-9 

23.9 
24.8 

9.9 

Rlood 

Chemical  Methods. — Chemical  methods  do  not  determine  the 
relative  availability  of  the  material,  but  distinguish  between  sub- 
stances of  high  and  of  low  availability.  Three  methods  have  been 
proposed : 

(1)  Digest  with  pepsin   hydrochloric   acid,   filter,   wash,   and 
determine  nitrogen  in  the  residue. 

(2)  Digest2  with  neutral  permanganate  of  potash  in  a  boiling 
water  bath,  filter,  wash,  and  determine  nitrogen  in  the  residue. 

(3)  Distil  with  caustic  soda  and  permanganate,  and  determine 
the  ammonia  which  passes  over. 

Each  of  these  methods  has  its  advantages  and  disadvantages. 
Method  (3)  is  not  applicable  to  cottonseed  meal.  All  the 
methods  depend  on  differences  in  the  resistance  of  the  various 
materials  to  the  reagents  employed. 

Influence  of  Conditions  on  Availability. — Various  conditions 
affect  the  availability  of  nitrogen  in  fertilizers,  such  as  acidity  of 
soils,  fineness  of  division  of  bone,  etc. 

Wheeler,3  in  an  unlimed  acid  soil,  found  the  availability  of 
blood  to  be  45.5,  and  ammonium  sulphate  injurious,  while  on  the 
same  soil  limed,  their  values  were  90.3  and  45.5  respectively. 
Johnson,  Jenkins,  and  Britton4  tested  the  availability  of  nitrogen 
in  bone  of  different  degrees  of  fineness;  for  meal  less  than  1/150 

1  Fraps,  Bulletin  106,  Texas  Station. 

2  See  Street,  Report  Connecticut  Exp.  Sta.,  1911,  Fertilizers,  p.  9. 

3  Bulletin  53,  Rh6de  Island  Station. 

4  Connecticut  State  Station  Report,  1897,  p.  257. 


SOURCES   AND   COMPOSITION    OF   FERTILIZERS  303 

inch,  compared  with  nitrate  of  soda  as  100,  it  was  11.3;  1/150  to 
1/50  inch,  8.5;  and  1/25  to  1/50,  5.6. 

Any  agency  which  accelerates  the  transformation  of  organic 
bodies  into  assimilable  compounds  would  increase  the  availability 
of  the  nitrogen.  The  temperature,  nature  of  soil,  and  activity  of 
the  organisms  in  the  soil  would  thus  be  of  effect. 

Agricultural  Value. — The  availability  of  a  nitrogenous  fer- 
tilizer is  measured  by  the  amount  of  nitrogen  which  plants  can 
secure  from  it  under  the  most  favorable  conditions.  Availability 
does  not  necessarily  represent  agricultural  value,  or  crop  produc- 
ing power  in  the  open  field,  since  other  factors  enter  in  the  ques- 
tion, some  of  which  are  as  follows : 

1 i )  Kind  of  Season. — In  a  very  wet  season,  nitrate  of  soda  is 
less  useful  than  other  forms  because  it  is  liable  to  be  washed  below 
the  reach  of  the  roots  and  lost  altogether  unless  applied  just  when 
needed,  or  on  a  heavy  soil. 

(2)  Kind  of  Crop. — Some  crops  grow  and  develop  quickly, 
while  others  grow  for  a  comparatively  long  period.     Quick-acting 
fertilizers  like  nitrate  of  soda  or  ammonium  sulphate,  would  be 
more  effective  on  the  former  than  organic  fertilizers,  which  must 
undergo  change  before  their  nitrogen  is  available.     The  slower- 
acting  organic  materials  would  be  better  for  plants  with  a  long 
growing  period,  unless  a  number  of  applications  of  the  quick- 
acting  fertilizers  are  made. 

(3)  Season  of  the  Year. — The  change  from  organic  nitrogen 
to  ammonia  or  nitrate  takes  place  more  readily  as  the  temperature 
approaches  98°   F.     Hence  the  organic  materials  would  be  re- 
latively less  effective  for  winter  crops  than  for  summer  ones.     A 
material  which  gives  excellent  results  when  applied  to  a  crop  dur- 
a  warm  and  moist  season,  might  be  very  unsatisfactory  when  the 
season  is  short,  cold,  and  dry. 

Phosphatic  Fertilizers. — Phosphatic  fertilizers  are  of  two  kinds, 
crude  phosphates,  and  treated  phosphates. 

Phosphates. — The  more  important  crude  phosphates  are  bone, 
bone  tankage,  bone  black,  rock  phosphate,  apatite,  and  Thomas 


304  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

phosphate.  Bat  guano  and  guano  ash  also  contain  phosphoric 
acid. 

Raw  bones  consist  of  mineral  matter,  which  is  chiefly  phos- 
phate of  lime,  and  organic  matter,  which  is  partly  fat  and  partly 
ossein,  a  nitrogenous  body.  The  ossein  decomposes  in  the  soil, 
and  increases  the  availability  of  the  phosphoric  acid  of  the  bone. 
Bone  contains  18  to  25  per  cent,  phosphoric  acid  and  3  to  5  per 
cent,  nitrogen. 

Raw  bone  meal  is  crushed  or  ground  bone  and  its  value  depends 
largely  upon  its  fineness  of  division.  The  more  finely  it  is 
ground,  the  more  rapid  its  action.  Bone  meal  is  a  good  fer- 
tilizer, but  acts  slowly. 

Steamed  bone  meal  is  made  from  bone  which  has  been  steamed 
to  remove  the  fat  and  the  nitrogenous  matter,  the  latter  being 
made  into  glue  or  gelatine.  The  steaming  makes  the  bone  soft 
and  crumbly,  and  the  phosphoric  acid  is  more  quickly  available 
than  in  raw  bone.  '  Steamed  bone  meal  contains  22  to  29  per  cent, 
phosphoric  acid  and  1.5  to  2.5  per  cent,  nitrogen. 

Bone  black  is  made  by  distilling  or  charring  bones  out  of  con- 
tact with  air.  It  consists  chiefly  of  phosphate  of  lime  and  char- 
coal, and  is  used  for  removing  the  coloring  matter  in  the  refining 
of  sugar.  It  contains  32  to  36  per  cent,  phosphoric  acid.  Spent 
bone  black  is  treated  with  sulphuric  acid  like  phosphate  rock. 

Rock  Phosphates. — Rock  phosphates  such  as  are  used  for 
manufacture  of  acid  phosphate  consist  chiefly  of  calcium  phos- 
phate, though  they  contain  a  small  amount  of  iron  and  alumina. 
They  are  found  in  South  Carolina  and  Florida  as  nodules, 
pebbles,  or  boulders,  and  in  Tennessee  in  veins  and  pockets. 
These  rock  phosphates  range  from  25  to  40  per  cent,  in  phos- 
phoric acid. 

Rock  phosphates  containing  excessive  amounts  of  carbonate  of 
lime  or  of  oxides  of  iron  or  alumina,  are  not  suitable  for  the 
manufacture  of  acid  phosphates,  though  they  may  be  used  for 
direct  application  to  the  soil.  The  carbonate  of  lime  consumes 
sulphuric  acid,  while  the  oxide  of  iron  and  alumina  react  with 
soluble  phosphates,  causing  them  to  revert. 


SOURCES  AND   COMPOSITION   OF 


305 


Rock  phosphate  is  used  to  a  certain  extent  as  a  fertilizer. 
When  ground  very  fine,  so  the  particles  may  float  in  the  air,  it  is 
known  as  floats.  It  does  not  act  as  quickly  as  acid  phosphate, 
and  may  give  little  results  the  first  year.  Some  soil  chemists1 
advocate  the  use  of  heavy  applications  of  ground  rock  phosphate, 
together  with  liberal  applications  of  manure  or  green  crops  plow- 


Fig.  72. — Mining  pebble  phosphate. 

ed  under,  for  staple  crops  like  corn.  According  to  the  Ohio  field 
experiments,  acid  phosphate  used  with  manure  gives  larger  net 
returns  than  rock  phosphate.2 

Apatite. — This  is  a  crystallized  calcium  phosphate  which  occurs 
in  quantity  in  Canada.  The  highest  grade  contains  40  per  cent. 
phosphoric  acid. 

1  Hopkins,  Soil  Fertility  and  Permanent  Agriculture,  p.  226. 

2  Circular  120,  Ohio  Station. 


306  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Thomas  phosphate  is  a  by-product  from  the  manufacture  of 
steel  from  phosphatic  pig  iron.  It  contains  15  to  20  per  cent, 
phosphoric  acid  in  connection  with  large  amounts  of  lime  and 
oxide  of  iron.  The  phosphoric  acid  was  believed  to  be  present 
as  tetra-calcium  phosphate,  but  according  to  Morison,1  it  is  a  silica 
phosphate  of  lime  and  ferrous  iron.  Thomas  slag  has  its  greatest 
effect  upon  soils  rich  in  organic  matter  and  poor  in  lime.  It  con- 
tains free  lime,  which  may  neutralize  soil  acids.  It  is  a  slow 
acting  fertilizer. 

Acid  Phosphate. — It  has  been  found  by  experiment  that  treat- 
ment, of  phosphates  with  sulphuric  acid  exerts  a  powerful  in- 
fluence upon  their  crop-producing  power,  and  immense  quantities 
are  so  treated  for  this  reason.  The  rock  is  first  ground  to  a 
powder,  and  treated  with  approximately  an  equal  weight  of  sul- 
phuric acid.  The  following  reaction  takes  place : 

(1)  Ca3P2O8  +  H2SO4  =  H3PO4  +  CaSO4. 

(2)  Ca3P208  +  4H3P04  ==  3CaH4  P2O8. 

Mono-calcium  phosphate  soluble  in  water  is  produced  from  cal- 
cium phosphate.  The  calcium  sulphate,  or  gypsum,  unites  with 
water  and  causes  the  mass  to  harden.  On  standing  the  following 
reaction  may  take  place,  di-calcium  phosphate  being  formed : 

(3)  CaH4P2Oa  +  Ca,P20,  =  2Ca2H2P2O8. 

This  process  is  called  reversion,  and  the  di-calcium  phosphate 
is  termed  reverted  phosphoric  acid.  Reversion  is  also  caused  by 
the  presence  of  iron  and  aluminium.  The  reaction  is  not  clearly 
understood  but  may  possibly  be  as  follows : 

(4)  2CaH4P208  +  Fe203  =  Fe,2P2O8  +  Ca,H2P2O8  +  3H2O. 
The  reverted  phosphoric  acid  is  assumed  to  have  a  value  equal 

to  water-soluble  phosphoric  acid.  It  is  also  termed  citrate-soluble 
phosphoric  acid,  since  it  is  dissolved  by  ammonium  citrate  in  the 
chemical  analysis  of  the  fertilizer.  Reversion  by  iron  oxide  and 
alumina  produces  ferric  or  alumina  phosphate,  both  of  which 
contain  the  phosphoric  acid  in  an  insoluble  form.  Some  alumina 
phosphates  are,  however,  citrate-soluble. 

Phosphoric  acid  is  thus  present  in  an  acid  phosphate  in  three 
1  Jour.  Agr.  Sci.,  1909,  p.  161. 


SOURCES  AND  COMPOSITION   OF   FERTILIZERS  307 

forms — water-soluble,  reverted,  and  insoluble.  Free  phosphoric 
acid  may  also  be  present.  The  insoluble  is  the  phosphoric  acid 
insoluble  in  water  and  in  neutral  ammonium  citrate.  It  is  either 
the  original  tri-calcium  phosphate  of  the  untreated  rock,  or  phos- 
phoric acid  which  as  reverted  to  the  insoluble  condition. 

When  the  rock  is  treated  with  an  excess  of  acid,  some  free 
phosphoric  acid  or  sulphuric  acid  is  present,  which  rots  the  bags 
and  also  causes  the  acid  phosphate  to  be  very  sticky,  especially  in 
moist  climates,  so  that  it  cannot  be  easily  drilled  in. 

Available  phosphoric  acid  is  the  sum  of  the  reverted  and  water- 
soluble.  In  speaking  of  an  acid  phosphate,  the  phosphoric  acid 
referred  to  is  the  available.  Thus,  if  we  speak  of  a  16  per  cent, 
acid  phosphate,  we  mean  that  it  is  guaranteed  to  contain  16  per 
cent,  of  available  phosphoric  acid,  regardless  of  the  total  quantity 
present.  Acid  phosphate  contains  12,  14,  or  16  per  cent,  available 
phosphoric  acid.  The  12  and  14  per  cent,  grades  are  often  made 
by  mixing  dirt  or  sand  with  the  16  per  cent,  phosphate.  Such  a 
mixture  is  not  an  acid  phosphate,  but  is  a  mixture  of  acid  phos- 
phate and  dirt  or  sand. 

Treated  phosphates  may  be  made  from  phosphate  rock,  apatite, 
bones,  bone  ash,  or  bone  black.  Whatever  the  original  material 
used,  equal  quantities  of  water-soluble  or  reverted  phosphoric 
acid  have  equal  values.  That  is  to  say,  the  water-soluble  acid 
produced  from  apatite  is  equal  in  value,  pound  for  pound,  to  that 
from  bones. 

Dissolved  bone  should  be  a  treated  phosphate  prepared  from 
bone.  It  should  contain  2  to  3  per  cent,  nitrogen.  Dissolved 
bone  black  is  prepared  from  bone  black. 

Superphosphates. — Concentrated  phosphates  are  prepared  for 
long  distance  shipments,  when  the  saving  of  transportation  will 
more  than  pay  the  extra  expense  of  manufacture.  High  grade 
phosphate  rock  is  treated  with  dilute  sulphuric  acid,  with  the  pro- 
duction of  calcium  sulphate  and  phosphoric  acid : 

Ca3(P04)2  +  3H2S04  =  3CaS04  +  2H3  PO4. 


308  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  calcium  sulphate  is  filtered  off,  the  solution  of  phosphoric 
acid  concentrated  and  then  mixed  with  phosphate  rock. 

Ca3(P04)2  +  4H3P04  =  3CaH4(P04)2. 

2Ca3(P04)2  +  2H3P04  =  3CaaH2(P04)2. 

The  product  contains  30  to  45  per  cent,  available  phosphoric 
acid,  depending  on  the  degree  of  concentration  of  the  acid  and 
the  kind  of  rock  used. 

Availability  of  Phosphatic  Fertilizers. — The  values  of  different 
forms  of  phosphoric  acid  are  compared  in  the  same  way  as  nitro- 
gen, namely,  plants  are  grown  under  such  conditions  that  phos- 
phates are  the  limiting  factor  and  a  comparison  made  of  the 
amounts  of  phosphoric  acid  taken  up  by  the  crops. 

The  availability  of  phosphoric  materials  depends  upon  other 
conditions  in  addition  to  the  form  of  combination  of  the  material, 
such  as  the  presence  of  carbonate  of  lime  or  some  other  sub- 
stances in  the  soil,  the  fineness  of  the  material,  the  nature  of  the 
plant,  etc.  The  effect  of  these  conditions  has  not  been  studied  to 
a  great  extent. 

Potash  Materials. — Potash  is  of  relatively  less  importance  than 
nitrogen  or  phosphoric  acid,  because  potash  is  more  abundant  in 
the  soil  than  either  nitrogen  or  phosphoric  acid,  and,  though 
larger  quantities  are  removed,  the  potash  is  more  likely  to  be  re- 
turned. The  potash  taken  up  is  most  largely  in  the  stems  and 
leaves  of  plants,  that  is,  the  portion  of  the  plant  which  is  gen- 
erally returned  to  the  soil  either  directly,  or  indirectly  in  manure. 
When  the  entire  crop  is  removed,  the  loss  of  potash  is  large. 
Potash  is  a  very  necessary  constituent  of  fertilizers  for  some  soils 
and  some  crops. 

The  chief  commercial  potash  materials  are  tobacco  stems,  wood 
ashes,  and  the  German  potash  salts,  kainit,  muriate  of  potash,  and 
sulphate  of  potash. 

Tobacco  stems  are  a  by-product  from  tobacco  factories.  They 
contain  6  to  8  per  cent,  potash,  2  to  2.5  per  cent,  nitrogen,  and  3 
to  5  per  cent,  phosphoric  acid.  They  are  used  largely  as  an 
insecticide,  but  may  sometimes  be  secured  for  a  sufficiently  low 
price  to  allow  their  use  as  a  fertilizer. 


SOURCES  AND  COMPOSITION   OF   FERTILIZERS 


309 


Wood  ashes  are  variable  in  composition,  and  their  value 
depends  upon  the  kind  of  wood  from  which  they  are  made,  and 
whether  they  are  leached  or  unleached.  Hard  wood  yields  the 
most  valuable  ash.  Ashes  exposed  to  the  weather  lose  most  of 
their  potash  by  leaching.  Unleached  ashes  contain  4  to  8  per 
cent,  potash  and  about  2  per  cent,  phosphoric  acid. 

Goessmann  gives  the  following  analyses  of  ashes : 


Average  per  cent. 

Unleached  — 
Potash  

2.5  to  10.2 
0.3  to    4.0 
18.0  to  50.0 

about    0.5 
about  40.0 
about    1.5 

5-5 
1-9 

34-0 

Phosphoric  acid  

L/ime  

Leached  — 
Potash  

Coal  ashes  contain  little  plant  food.  Since  ashes  contain  car- 
bonate of  lime  and  carbonate  of  potash,  they  are  especially  bene- 
ficial to  acid  soils,  or  those  needing  lime. 

German  Potash  Salts. — The  German  potash  salts  are  mined  and 
concentrated  in  the  region  around  Strassfurt,  Germany,  where 
they  occur  in  immense  beds  at  depths  of  from  1500  to  2500  feet 
below  the  surface.  The  important  minerals  found  are  as 
follows : 

Carnallite,  KC1,  MgCl2,  6ELO. 

Kainit,  K2SO4,  MgSO4,  MgCL,,  2H2O. 

Sylvinite,  KC1,  NaCl,  K2SO4,  MgCl2,  6H2O,  MgSO4. 

Hartsalz,  KC1,  NaCl,  MgSO4,  H2O." 

Carnallite,  the  chief  source  of  potash,  usually  occurs  mixed  with 
rock  salt  and  other  minerals,  and  contains,  as  mined,  about  9  per 
cent,  potash.  Kainit,  as  mined,  contains  about  30  per  cent,  rock 
salt  and  about  12  per  cent,  potash.  Sylvinite  is  a  mixture  of 
sodium  and  potassium  chlorides,  containing  14  to  18  per  cent, 
potash.  The  potash  salts  chiefly  used  in  this  country  are  kainit, 
muriate  of  potash,  and  sulphate  of  potash. 


3IO  PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

Kainit,  correctly  speaking,  is  a  mineral  composed  of  sulphate 
of  potash  and  magnesia,  K2SO4,  MgSO4,  MgCl2,  6H2O.  The 
term  is  also  used  for  crude  potash  salts  containing  not  less  than 
12.4  per  cent,  potash,  which  may  be  crude  kainit  or  mixtures  of 
other  crude  salts.  Since  kainit  is  prepared  from  crude  salts,  no 
expense  of  manufacturing  is  attached  to  it.  On  the  other  hand, 
freight  per  unit  of  potash  is  higher  than  for  the  more 
concentrated  potash  salts.  At  a  distance  from  the  mines, 
the  freight  cost  is  greater  than  the  manufacturing  cost, 
so  that  the  concentrated  salts  are  cheaper.  Since  kainit  contains 
chlorides,  it  is  not  suitable  for  use  on  tobacco  or  potatoes.  Kainit 
is  used  as  a  preservative  in  saving  stable  manure,  to  check  attacks 
of  injurious  insects,  and  as  a  remedy  against  cotton  rust. 

Muriate  of  potash  is  a  concentrated  potash  salt  prepared  from 
the  crude  potash  minerals  by  solution  and  crystallization.  Various 
grades  are  prepared,  ranging  from  70  to  98  per  cent,  muriate  of 
potash  equivalent  to  46.7  to  62  per  cent,  potash  (K2O). 

Sulphate  of  potash  is  prepared  by  reaction  between  the  muriate 
of  potash  and.  sulphate  of  magnesia,  also  found  in  the  potash 
mines.  The  two  are  mixed  in  solution,  and  the  sulphate  of 
potash,  being  less  soluble,  separates  out.  Various  grades  are 
prepared,  containing  45  to  53  per  cent,  potash  (K2O). 
2KC1  +  MgSO4  =  K2SO4  +  MgCL, 

Double  Manure  Salts. — This  is  an  impure  sulphate  of  potash 
containing  about  30  per  cent,  potash.  It  contains  considerable 
amounts  of  sulphate  of  magnesia. 

Forms  of  Potash. — The  compounds  of  potash  used  in  fer- 
tilizers are  all  soluble  in  water,  and  there  is  practically  little  differ- 
ence in  their  availability.  Some  forms  are,  however,  better 
adapted  to  some  crops  than  others.  Fertilizers  free  from 
chlorides  are  desirable  for  potatoes  and  tobacco,  since  chlorides 
make  the  potato  less  mealy  and  injure  the  burning  quality  of  the 
tobacco. 

Miscellaneous  Fertilizing  Materials. — The  analyses  of  some  mis- 
cellaneous fertilizing  materials  are  given  in  the  table.  Most  of 


SOURCES  AND  COMPOSITION   OF   FERTILIZERS 


them  are  very  variable  in  composition,  but  may  furnish  cheap 
sources  of  plant  food. 


Phosphoric 
acid 

%  Nitrogen 

Potash 

Per  cent. 

Per  cent. 

Per  cent. 

2  O-2   *\ 

.u     4-u 

2   C-    8  O 

.u-   ^.u 

1   O-    I    *\ 

o  ^-O  8 

Q  c_  o  8 

20-       -1     Q 

I  o-l  6 

i  o-  i  6 

O  2 

o  o^ 

OC 

Mussels   fresh  

O  Q 

O  12 

i  "* 

2  Q 

WooH    a«;he«; 

u.j     4.^ 

••O 

u-o 

CHAPTER  XVI. 


PURCHASE  AND  USE  OF  FERTILIZERS. 

Commercial  fertilizers  consist;  first,  of  acid  phosphate,  cotton- 
seed meal,  potash  salts,  and  other  commercial  substances  contain- 
ing plant  food;  and  secondly,  of  mixtures  of  these  substances, 
made  to  secure  a  product  of  a  desired  composition.  The  mixture 
usually  contains  all  three  kinds  of  plant  food,  though  a  number  of 
mixtures  are  on  the  market  which  contain  only  two,  phosphoric 
acid  and  potash,  or  phosphoric  acid  and  nitrogen. 

Mixed  Fertilizers. — Mixed  fertilizers  are  of  two  classes — dry 
mixed  and  wet  mixed.  In  dry  mixing,  the  materials  are  weighed 
out,  ground  when  necessary,  mixed  thoroughly,  then  passed 
through  a  screen  so  as  to  make  them  of  uniform  size.  The  nitro- 
gen is  generally  in  two  or  more  forms,  one  highly  available,  the 
others  less  so.  A  filler  is  added  when  the  sum  total  of  the  in- 
gredients containing  plant  food  do  not  make  up  the  required 
weight  to  give  the  desired  composition.  Any  substance  which 
contains  no  plant  food,  or  quantities  much  lower  than  the  content 
of  standard  fertilizer  ingredients,  should  be  considered  as  a  filler. 
The  filler  is  usually  sand  or  dirt,  but  sometimes  objectional  fillers 
are  used,  such  as  limestone,  lime,  or  pyrite  cinder,  which  con- 
tains oxide  of  iron.  Small  quantities  of  lime  are  sometimes  used 
to  dry  the  fertilizer. 

In  wet  mixing,  the  organic  nitrogenous  material  is  first  mixed 
with  the  sulphuric  acid,  then  the  phosphate  rock  is  added,  and  the 
mixture  is  dumped  out  and  allowed  to  harden  as  in  the  manu- 
facture of  acid  phosphate.  Potash  salts  or  nitrate  of  soda,  if 
either  is  used,  is  added  while  the  product  is  being  ground  or 
otherwise  prepared.  In  wet  mixing,  the  nitrogenous  material  is 
to  a  certain  extent  acted  on  by  the  acid.  There  is  no  doubt  that 
this  treatment  increases  the  availability  of  low-grade  nitrogenous 
materials,  but  little  experimental  work  has  been  done  to  show  the 
availability  of  the  product.  Street1  found  the  following  changes 
in  the  nitrogen  of  one  sample  commercially  treated  in  this  way : 
1  Report  Connecticut  Exp.  Sta.,  1911,  p.  14. 


PURCHASE  AND   USE   OF   FERTILIZERS 


313 


• 

Before 
treating 

After 
treating 
(two  days) 

Ammonia  nitrogen  

6   r 

\Va.ter-soluble  organic  nitrogen  

°»o 

7  8 

J4-3 

\Vater  insoluble  organic  nitrogen   

gc  7 

O/'/ 

28  o 

°O-/ 

In  a  pot  experiment  on  oats  and  millet  the  treated  nitrogenous 
material  had  an  availability  of  66  compared  with  that  of  nitrate 
of  soda  as  100,  cottonseed  meal  47,  hair  waste  29,  garbage  tank- 
age 28,  and  peat  4. 

Guarantee  of  Fertilizer. — A  fertilizer  is  valuable  on  account 
of  the  quantity  and  kind  of  plant  food  it  contains.  The  manu- 
facturer buys  on  analysis,  that  is,  he  pays  on  the  basis  of  the 
chemist's  analysis  of  a  fair  sample  of  the  shipment.  The  in- 
dividual farmer,  or  one  who  purchases  on  a  small  scale,  cannot 
afford  to  pay  for  a  chemical  analysis  and  can  tell  little  or  nothing 
about  the  substance  by  inspection.  Hence  the  laws  of  most  States 
in  which  fertilizers  are  used,  provide  for  a  guarantee  of  com- 
position, penalties  for  failure  to  deliver  guaranteed  ingredients, 
and  officials  who  are  charged  with  the  inspection  and  analysis  of 
fertilizers.  The  simplest  guarantee  consists  of  a  statement  of  the 
guaranteed  minimum  percentages  of  the  available  or  total  phos- 
phoric acid,  the  nitrogen,  and  the  potash.  The  total  phosphoric 
acid  is  guaranteed  only  with  respect  to  bone  meal  or  rock  phos- 
phate, which  contain  little  "available"  according  to  chemical 
methods. 

In  some  States,  the  term  ammonia  is  used  instead  of  nitrogen, 
and  in  one  or  two  States,  phosphorus  and  potassium  instead  of 
phosphoric  acid  and  potash.  Otherwise  the  latter  terms  are  used 
the  world  over.  A  a  varying  guarantee,  such  as  "2  to  3  per  cent, 
potash,"  is  allowed  in  some  States,  but  is  not  desirable.  Other 
States  require  a  guarantee  of  water-soluble  and  reverted  phos- 
phoric acid.  The  use  of  the  terms  "potash  as  sulphate"  etc., 
allowed  in  some  States,  is  confusing  to  the  average  purchaser. 
21 


314  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Commercial  Valuation. — The  commercial  value  of  a  fertilizer  is 
the  selling  price  of  the  plant  food  ingredients  as  determined  by 
market  and  trade  conditions.  The  agricultural  value,  or  crop- 
producing  power,  often  has  no  relation  to  the  commercial  or  mar- 
ket value  of  the  material.  Thus  it  frequently  happens  that  an 
element  costs  less  in  a  highly  available  form  than  in  a  less  avail- 
able form.  Organic  nitrogen  may  cost  more  than  nitric  nitrogen, 
while  the  nitric  nitrogen  is  more  available  and  would  have  a 
greater  crop-producing  power  if  properly  applied. 

The  commercial  value  is  usually  fixed  by  the  cost  of  the  plant 
food  in  the  raw  materials  in  ton  lots  at  retail,  and  frequently  at 
the  seaboard.  Cost  of  transportation  must  be  added.  Fluctua- 
tions in  the  values  take  place  according  to  trade  conditions. 

An  illustration  of  the  commercial  value  is  as  follows :  Suppose 
that  14  per  cent,  phosphoric  acid  costs  $16.80  a  ton.  A  ton  con- 
tains 14x20  =  280  pounds  available  phosphoric  acid,  so  that  one 
pound  costs  6.0  cents.  This  is  the  commercial  or  trade  value. 

If  the  commercial  valuation  of  phosphoric  acid  is  6  cents, 
potash  6  cents  and  nitrogen  20  cents,  it  does  not  follow  that  a 
pound  of  nitrogen  will  give  an  increase  of  crop  worth  20  cents, 
or  that  a  pound  of  phosphoric  acid  will  give  a  6  cent  increase,  or 
that  the  effect  will  be  in  that  ratio. 

1911 

Cents  per  pound 

Nitrogen  in  nitrates 16.0 

Nitrogen  in  ammonia  salts 16.0 

Organic  nitrogen  in  dry  and  fine  ground  fish  and  blood-  •  •  23.0 

Organic  nitrogen  in  cottonseed  meal  and  castor  pomace-  •  •  21.0 
Organic  nitrogen  in  fine  ground  bone  and  tankage  and 

mixed  fertilizers 20.0 

Organic  nitrogen  in  coarse  bone  and  tankage 15.0 

Phosphoric  acid  soluble  in  water 4.5 

Phosphoric  acid  soluble  in  ammonium  citrate 4.0 

Phosphoric  acid  in  fine  ground  bone  and  tankage 4.0 

Phosphoric  acid  in  coarse  bone  and  tankage 3.5 

Phosphoric   acid  insoluble  (in  water  and  in  ammonium 

citrate )  in  mixed  fertilizers 2.0 

Potash  in  high  grade  sulphate  and  in  mixtures  free  from 

muriate  (chloride) 5.0 

Potash  as  muriate 4.5 

Potash  in  cottonseed  meal  and  castor  pomace   5.0 


PURCHASE  AND   USE   OF   FERTILIZERS  315 

The  preceding  schedule  of  trade  values  is  the  one  agreed  upon 
by  the  Experiment  Stations  of  Massachusetts,  Rhode  Island, 
Connecticut,  New  Jersey,  and  Vermont,  after  a  careful  study  of 
prices  ruling  in  the  larger  markets  of  the  southern  New  England 
and  middle  States.1 

These  trade  values  are,  as  nearly  as  can  be  estimated,  the 
average  figures  at  which,  in  the  six  months  preceding  March  i, 
1911,  the  respective  unmixed  ingredients  could  be  bought  at  retail 
for  cash  in  the  larger  markets  (Boston,  New  York,  etc.)  They 
also  correspond  to  the  average  wholesale  prices  for  six  months 
ending  March  ist,  plus  about  20  per  cent,  in  the  case  of  goods  for 
which  there  are  wholesale  quotations.  The  valuations  obtained  by 
the  use  of  the  above  figures,  it  is  claimed,  will  be  found  to  agree 
fairly  with  the  reasonable  average  retail  price  in  the  large  mar- 
kets of  standard  raw  materials,  such  as  nitrate  of  soda,  sulphate 
of  ammonia,  dried  blood,  cottonseed  meal,  acid  phosphate, 
muriate  of  potash,  and  sulphate  of  potash,  etc. 

The  valuations  used  in  Texas2  for  the  season  of  1911-12  are 
as  follows : 

Cents  per  pound 

Available  phosphoric  acid 6 

Total  phosphoric  acid  in  bone  and  tankage 4 

Nitrogen  in  mixed  fertilizers,  bat  guano  and  cottonseed  meal    20 

Nitrogen  in  tankage 18 

Potash 6 

The  valuation  of  nitrogen  in  Texas  depends  largely  on  the 
cost  of  cottonseed  meal. 

Calculation  of  Commercial  Valuation. — Two  methods  are  used, 
namely,  the  pound  method  and  the  unit  method. 

(o>)  The  Pound  Method. — Calculate  the  number  of  pounds  of 
each  ingredient  per  ton  and  multiply  by  the  cost  per  pound.  For 
example,  in  an  8.00  -  1.65  -  2.00  fertilizer: 

0.08      X  2,000  =  160  pounds  X     6  cents-. =    $9-6o 

0.0165  X  2,000  = :     33  pounds  X  20  cents =        6.60 

0.02      X  2,000  =    40  pounds  X     6  cents =       2.40 

Valuation  per  ton $21.60 

1  Report  Connecticut  Exp.  Sta.,  1911,  p.  7. 

2  Texas  Station  Bulletin  No.  149. 


316  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

(b)  The  Unit  Method. — A  unit  is  i  per  cent.,  and  i  per  cent, 
of  a  ton  is  20  pounds.  Hence  20  times  the  value  of  a  pound  gives 
the  value  of  a  unit.  To  calculate  the  valuation,  multiply  per- 
centage by  value  per  unit.  With  nitrogen  at  20  cents  a  pound,  a 
unit  costs  $4.00.  With  potash  at  6  cents,  the  unit  costs  $1.20. 
Using  the  example  given  above: 

8.0     X  $1.20 =  $9.60 

1.65    X      4-0° -         2.60 

2.0      X       1-20 =      2.40 

Valuation  per  ton $21.60 

The  Meaning  of  Commercial  Valuation. — The  valuation  of  a 
brand  of  fertilizer  by  the  State  Fertilizer  Control  does  not  repre- 
sent its  proper  selling  price  at  the  point  of  consumption.  Neither 
should  it  be  inferred  that  the  ingredients  in  the  brand  in  question 
have  of  necessity  the  commercial  value  indicated.  It  may  be  greater 
or  less  than  is  shown.  The  valuation  system  is  based  on  the  as- 
sumption that  all  brands  compared  are  solely  of  high  grade  in- 
gredients, an  assumption  which  may  be  erroneous.  "Valuations" 
should  not  be  construed  as  showing  the  commercial  worth  of  a 
given  fertilizer,  but  the  retail  trade  value  at  the  seaboard,  of 
amounts  of  nitrogen,  phosphoric  acid,  and  potash,  equal  to  those 
contained  in  a  ton  of  the  brand  in  question,  in  unmixed,  standard 
raw  materials  of  good  quality. 

Valuations  thus  construed,  while  not  infallible,  are  helpful : 

(a)  To  show  whether  a  given  fertilizer  is  worth  its  cost  from 
the  commercial  standpoint. 

(b)  As  a  common  basis  on  which  to  compare  the  commercial 
value  of  different  brands,  enabling  buyers  to  note  whether  prices 
asked  are  warranted  by  values  contained,  and  aiding  buyers  to 
secure  the  most  value  for  the  least  money. 

Agricultural  Value. — The  agricultural  value  of  a  fertilizer  is 
measured  by  the  value  of  the  increased  crop  produced  by  its  use. 
It  is  variable,  depending  upon  the  availability  of  the  constituent, 
the  value  of  the  crop,  the  needs  of  the  soil,  weather  conditions, 
etc.  For  example,  the  agricultural  value  of  a  pound  of  water- 
soluble  phosphoric  acid  is  likely  to  be  greater  than  that  of 


PURCHASE   AND  USE   OF   FERTILIZERS 


317 


an  equal  amount  of  insoluble  phosphoric  acid,  when  used  under 
the  same  conditions,  because  it  is  much  more  easily  used  by  plants. 
But  the  water-soluble  phosphoric  acid  may  produce  an  increased 
yield  of  a  crop  on  some  soils  and  still  not  cause  an  increase  in 
value  sufficient  to  pay  the  cost  of  the  application,  while  on  an- 
other crop  the  application  may  result  in  a  very  great  increase  in 
value.  On  a  soil  which  needs  phosphoric  acid  its  use  may  be 
profitable,  while  on  one  which  does  not  need  this  form  of  plant 
food,  it  will  have  no  effect.  A  fertilizer  may  produce  a  com- 
paratively small  effect  upon  a  crop  of  high  selling  price,  and  yet 
be  profitable ;  while  on  a  crop  of  low  selling  price  the  increase  may 
not  offset  the  cost  of  the  fertilizer. 

Basis  of  Purchase. — Large  sales  of  fertilizing  material  are 
usually  at  a  certain  price  per  unit.  A  unit  means  one  per  cent,  on 
the  basis  of  a  ton.  That  is  20  pounds.  For  example,  $1.00  per 
unit  for  phosphoric  acid  would  be  $1.00  for  20  pounds,  or  5  cents 
per  pound. 

The  ton  basis  of  purchase  is  used  for  the  sale  of  manufactured 
fertilizers.  The  purchaser  must  consider  the  guarantee,  and 
valuation  of  the  fertilizer  before  purchasing.  For  example,  sup- 
pose fertilizer  A  is  offered  for  $21.00  a  ton,  and  fertilizer  B  for 
$24.00  a  ton : 


A 

B 

Per  cent. 

1-5 
6.00 

I.OO 

Per  cent. 
2.00 

8.00 

2.00 

Potash  

Taking  the  valuations  given  elsewhere,  we  have  the  following : 


A 

B 

$6  oo 

$8  oo 

Available  phosphoric  acid.  (6  cents)  

Total 

#14.40 

PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


There  is  thus  a  difference  of  $3.00  in  the  price  and  $5.60  in  the 
valuation.  Fertilizer  B  contains  more  value  for  the  money.  But 
the  purchaser  must  consider  the  needs  of  his  crop  and  his  soil 
also,  and  not  seek  to  secure  merely  the  most  value  for  the  least 
money. 

Home  Mixing  of  Fertilizers. — By  home  mixing  of  fertilizers, 
we  mean  the  purchase  of  the  ingredients,  and  mixing  them  in  the 
proportions  to  form  the  fertilizer  desired.  The  preparation  of 
acid  phosphate  from  phosphate  rock,  or  the  grinding  of  bones  or 


Fig-  73- — Instructing  negro  students  in  the  home  mixing  of  fertilizers. 

other  hard  material,  is  most  economically  conducted  on  a  large 
scale.  In  home  mixing,  then,  we  simply  mix  the  ingredients 
which  have  already  been  prepared  by  grinding  or  otherwise. 

The  operation  is  very  simple,  the  apparatus  required  being  a 
clean  floor,  one  or  two  shovels,  and  a  sand  screen,  with  meshes 
of  about  4  to  an  inch.  The  materials  are  first  weighed  out,  one 
by  one,  and  piled  on  the  floor,  any  large  lumps  being  broken  down 


PURCHASE    AND   USE   OF   FERTILIZERS  319 

with  a  shovel.  The  pile  is  then  shoveled  over  several  times,  and 
the  mixture  passed  through  the  screen.  Any  lumps  which  fail 
to  pass  the  screen  are  beaten  up,  and  added  to  the  mixture.  The 
mixture  is  then  shoveled  over  several  times  more.  It  is  possible 
to  prepare  the  mixture  without  any  screen,  but  better  results  are 
secured  with  it. 

The  question  whether  home  mixtures  equal  factory  mixtures 
has  been  studied  bv  a  number  of  Experiment  Stations  in  the  fol- 
lowing way :  Samples  of  mixed  fertilizer  prepared  at  home  were 
secured,  and  examined  as  to  mechanical  character,  and  the  chem- 
ical composition  was  compared  with  that  calculated  from  the 
amount  and  composition  of  the  ingredients  used.  The  mechanical 
condition  was,  as  a  rule,  good  and  the  chemical  composition  did 
not  vary  to  any  greater  extent  than  samples  of  factory  mixed 
goods  as  sold  on  the  market.  The  New  Jersey  Experiment 
Station1  says  that  it  amply  demonstrated  in  1893,  and  corrobor- 
ated in  1894,  that  farmers,  with  their  ordinary  farm  appliances, 
can  prepare  mixtures  that  compare  very  favorably  with  pur- 
chased mixtures,  both  in  mechanical  condition  and  chemical  com- 
position. The  Vermont  and  Maine  Experiment  Stations  make 
similar  statements.  The  Ohio  Experiment  Station2  compared 
factory  mixed  goods  with  ready  mixed  goods  in  field  experi- 
ments, on  corn  and  wheat  and  found  that  the  home  mixed  goods 
gave  as  good  results  as  the  factory  mixed,  or  better.  The  New 
Hampshire  Experiment  Station3  secured  a  similar  result  on 
potatoes.  These  experiments  show  that  complete  fertilizers  can 
be  prepared  by  home  mixing,  which  are  equal  in  every  respect 
to  the  purchased  article.  It  might  sometimes  happen  that  a  mix- 
ture is  difficult  to  prepare,  owing  to  the  fact  that  the  materials 
have  become  lumpy  and  hard  to  beat  up,  but  this  is  the  exception 
and  not  the  rule. 

Whether  or  not  it  is  profitable  to  make  home  mixtures  depends 
upon  the  conditions.  It  is  certainly  more  economical  to  buy  the 

1  Bulletin  No.  113. 

2  Bulletin  No.  100. 

3  Bulletin  No.  in. 


32O  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

unmixed  materials  in  large  lots  for  cash,  and  make  mixtures,  than 
to  purchase  mixed  goods  at  retail,  especially  at  credit  prices.  In 
this  way  one  can  secure  somewhat  more  plant  food  for  $20.00, 
than  can  be  secured  for  $30.00,  in  a  mixed  fertilizer.  The  Ex- 
periment Stations  of  New  York,  Connecticut,  New  Jersey,  North 
Carolina,  and  other  States  have  demonstrated  this  to  be  a  fact. 
When  the  unmixed  materials  are  purchased  in  small  quantity,  at 
retail,  it  may  or  may  not  be  profitable  to  make  home  mixtures. 
One  can  easily  decide  this  question  for  himself  by  securing  prices 
on  mixed  goods,  and  calculating  the  amount  he  would  have  to 
pay  for  the  unmixed  materials  to  make  the  same  mixture. 

Mixed  fertilizers  purchased  direct  from  the  manufacturer  in 
carload  lots  may  often  be  secured  more  cheaply  than  the  home 
mixture  can  be  made,  since  the  cost  of  mixing  is  less  to  the  manu- 
facturer, who  has  appliances  for  economically  handling  large 
quantities. 

It  may  be  said  further  in  favor  of  home  mixtures,  that  one  can 
know  exactly  what  ingredients  are  used,  whether  they  are  of  high, 
medium,  or  low  grade.  It  is  also  easy  to  vary  the  mixture  as  de- 
sired, and  to  test  the  effect  of  different  combinations  upon  the 
soil. 

It  has  been  objected  to  home  mixing  that  the  materials  may  not 
always  be  easily  secured  and  that  the  mechanical  condition  is 
not  as  perfect  as  in  the  commercial  mixed  fertilizer.  Mixed  fer- 
tilizers are  widely  distributed  and  easily  secured. 

Calculating  the  Ingredients  of  a  Mixture. — The  calculation  of 
the  ingredients  to  make  a  fertilizer  of  a  desired  composition,  is  a 
simple  mathematical  matter.  It  is  necessary,  of  course,  to  know 
the  composition  of  the  ingredients  to  be  used.  Suppose  it  is 
desired  to  make  a  fertilizer  containing  8  per  cent,  available  phos- 
phoric acid,  2  per  cent,  nitrogen  and  2  per  cent,  potash,  using  acid 
phosphate  containing  14  per  cent,  available  phosphoric  acid, 
kainit  containing  12  per  cent,  potash,  and  cottonseed  meal  con- 
taining /  per  cent,  nitrogen,  2  per  cent,  available  phosphoric  acid, 
and  1.5  per  cent,  potash. 


PURCHASE:  AND  USE  OF  FERTILIZERS  321 

The  desired  fertilizer  would  contain,  in  1,000  pounds,  80 
pounds  available  phosphoric  acid,  20  pounds  nitrogen,  and  20 
pounds  potash. 

Since  i  pound  cottonseed  meal  contains  0.07  pounds  nitrogen, 
it  would  take  20  -•-  0.07  =  286  pounds  cottonseed  meal  to  furnish 
20  pounds  nitrogen.  This  286  pounds  would  contain  also 
286  X  0.02  =  5.7  pounds  phosphoric  acid  and  286  X  i-5  =  4-3 
pounds  potash. 

The  80  pounds  available  phosphoric  acid  required,  less  5.7 
pounds,  in  the  cottonseed  meal,  leaves  74.3  pounds  to  be  secured 
from  the  acid  phosphate.  74.3  -f-  0.14  =  531  pounds  acid  phos- 
phate. 

The  20  pounds  potash  required,  less  4.3  pounds  in  the  cotton- 
seed meal,  leaves  15.7  pounds  to  be  secured  from  the  kainit. 
15.7  -r-  0.12  =  131  pounds  kainit. 

Then  the  desired  ingredients  to  make  1,000  pounds  of  the 
fertilizer,  would  consist  of : 

Pounds 

Cottonseed  meal 286 

Acid  phosphate 531 

Kainit    131 

Total    » 948 

Filler 52 


I  ,OOO 

It  would  thus  be  necessary  to  add  52  pounds  filler  to  make  the 
desired  composition. 

The  ingredients  for  other  fertilizer  mixtures  may  be  calculated 
in  a  similar  way.  In  factory  work,  it  is  necessary  to  allow  for 
variations  in  the  composition  of  the  ingredients  by  providing  for 
a  slight  over-run.  Otherwise,  some  of  the  mixtures  may  fall  be- 
low guarantee. 

Incompatibles  in  Fertilizer  Mixtures. — Certain  materials  should 
not  be  mixed  in  making  fertilizers,  for  the  following  reasons : 

( i )  Chemical  reactions  take  place  which  result  in  the  loss  of 
nitrogen  in  the  form  of  ammonia.  For  this  reason,  ammonium 
sulphate,  guano,  or  barnyard  manure  should  not  be  mixed  with 
lime,  ashes,  or  Thomas  slag. 


322  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

(NHJ2S04  +  Ca(OH)2  =:  2NH8  +  CaSO4  +  2H2O.  • 

(2)  Chemical  changes  convert  the  phosphoric  acid   into  less 
soluble  forms.  Acid  phosphate  should  not  be  mixed  with  Thomas 
slag,  lime  or  ashes. 

CaH4(PO4)2  -f  2CaO  ==  Ca3  PO4  +  2H2O. 
Lime  is,  however,  sometimes  mixed  with  moist  acid  phosphate 
to  improve  its  physical  condition,  so  that  the  resulting  mixture 
may  be  applied  with  a  fertilizer  drill. 

(3)  Certain  mixtures  will  harden  or  cake  and  thus  become 
difficult  to  distribute  if  kept  for  some  time  after  mixing.     Hence 
they  should  be  applied  soon  after  mixing.     This  applies  to  mix- 
tures of  lime  or  Thomas  slag  with  potash  salts,  nitrate  of  soda, 
and  kainit. 

Conditions  which  Modify  Use  of  Fertilizers. — These  are  :  ( i ) 
Deficiency  of  soil;  (2)  Value  of  crop;  (3)  Character  of  crop; 
(4)  Kind  of  rotation. 

Deficiency  of  Soil. — A  knowledge  of  the  nature  of  soils  with 
respect  to  the  deficient  elements  is  important,  in  order  that  those 
elements  which  are  present  in  abundance  may  not  be  added  to,  but 
that  they  may  be  supplemented  by  such  quantities  of  the  deficient 
elements  as  to  permit  maximum  profitable  crops.  This  matter 
of  soil  deficiencies  has  been  treated  elsewhere. 

An  opinion  as  to  the  deficiency  of  the  soil  may  be  based  on : 

(a)   The  chemical  composition  of  the  soil. 
(&)   The  behavior  of  the  crop. 

(c)  Previous  experience  in  the  use  of  fertilizers. 

(d)  Field  tests  to  ascertain  needs  of  the  soil. 

The  value  of  the  crop  is  of  importance  in  deciding  the  profit- 
able application  of  fertilizers.  Crops  may  roughly  be  divided  into 
two  classes :  the  first  class  have  a  relatively  low  commercial  value 
per  acre,  the  second  have  a  high  commercial  value  per  acre. 

Wheat,  corn,  oats,  cotton,  etc.,,  belong  to  the  first  class.  These 
crops  remove  large  amounts  of  plant  food  in  proportion  to  their 
value.  For  example,  a  ton  of  wheat  removes  38  pounds  of  nitro- 
gen, 19  pounds  phosphoric  acid,  and  13  pounds  of  potash.  With 
nitrogen  at  20  cents  and  phosphoric  acid  and  potash  at  6  cents,  the 


PURCHASE:  AND  USE  OF  FERTILIZERS 


3^3 


Fig-  74-— Corn  grown  (A)  continuously,  (B)  in  five  year  rotation. 
Minnesota  Station. 


324  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

value  of  this  plant  food  would  be  $9.50.  Wheat  at  $1.00  per 
bushel  would  bring  $33.33  per  ton.  The  value  of  plant  food  in 
the  grain  is  thus  nearly  y$  the  selling  price  of  the  crop.  Economy 
in  the  application  of  fertilizers  is  essential  to  profit  with  such  crops. 
Nitrogen  should  be  secured  as  much  as  possible  from  the  air  by 
legumes.  Application  of  fertilizers  should  be  based  largely  upon 
the  needs  of  the  soil. 

Onions,  asparagus,  melons,  cabbage,  and  tomatoes,  are  ex- 
amples of  crops  which  have  a  high  value  per  acre.  Such  plants 
may  be  fertilized  liberally,  since  the  cost  of  even  large  applications 
of  fertilizer  is  in  small  proportion  to  the  value  of  the  crop. 
Manure  or  legumes  turned  under  should  also  be  used  on  account 
of  their  beneficial  effect  on  the  soil. 

Character  of  the  Crop. — Plants  vary  in  the  quantity  of  plant 
food  needed  and  in  their  ability  to  secure  it.  The  season  of 
growth  is  also  of  significance,  since  plants  growing  during  the 
cooler  period  of  the  year  are  supplied  with  less  nitrogen  by  the 
soil  than  those  growing  during  the  warm  season. 

While  each  plant  possesses  individual  characteristics  which 
distinguish  it  from  others,  they  may  be  divided  into  groups  which 
have  somewhat  similar  characteristics,  particularly  as  regards 
method  and  time  of  growth  and  their  capacity  for  acquiring  food 
from  soil  sources. 

The  cereals  have  a  wide  root  growth  and  are  able  to  acquire 
food  from  insoluble  phosphates  and  potash  readily.  As,  with  the 
exception  of  Indian  corn,  their  development  takes  place 
early  in  the  summer  before  conditions  are  favorable  for  rapid 
nitrification,  they  are  particularly  benefited  by  nitrates.  Corn 
does  not  usually  require  as  large  proportions  of  nitrogen  as  of 
mineral  constituents,  as  its  growth  is  made  in  the  summer  while 
the  conditions  are  very  favorable  for  nitrates. 

The  grasses  resemble  the  cereals  in  their  power  of  acquiring 
mineral  food  and  are  also  benefited  by  application  of  nitrogen. 

The  clovers  readily  acquire  mineral  food,  and  also  take  nitro- 
gen from  the  air. 


PURCHASE:  AND  USE  OF  FERTILIZERS  325 

Root  crops  (beets,  mangels,  turnips,  carrots,  Irish  and  sweet 
potatoes)  cannot  make  ready  use  of  the  mineral  constituents  of 
the  soil.  Phosphates  are  especially  useful  for  turnips,  while  beets 
and  carrots  require  more  nitrogen.  Potash  is  particularly  useful 
to  potatoes. 

Market  garden  crops  have  a  high  commercial  value  with  a  low 
fertility  content.  Hence  they  can  be  profitably  supplied  with  an 
abundance  of  plant  food.  This  supply  also  increases  rapidity  of 
growth,  which  is  desirable,  as  the  price  is  often  in  proportion  to 
their  earliness. 

Fruit  crops  have  a  longer  season  of  preparation  and  growth, 
and  require  a  constant  transfer  of  food  from  the  tree  to  the  fruit 
during  the  growing  season.  Food  that  will  encourage  a  slow  and 
continuous  growth,  rather  than  a  quick  one,  is  required. 

The  Kind  of  Rotation. — The  order  in  which  the  crops 
follow  one  another  in  rotation,  the  kind  of  crop  previously  grown, 
and  the  treatment  given  it,  are  factors  in  intelligent  fertilization. 
If  the  previous  crop  is  a  legume,  and  has  left  considerable 
residues,  the  succeeding  crop  stands  less  in  need  of  nitrogenous 
fertilizers.  A  crop  succeeding  an  exhaustive  crop  not  liberally 
fertilized,  may  require  liberal  applications  of  plant  food.  The 
further  removed  the  crop  is  from  the  legume  crop,  the  greater 
its  probable  needs  of  nitrogenous  fertilization. 

Effect  of  Phosphoric  Agid,  Potash  and  Nitrogen  on  Plant 
Growth. — While  the  entire  plant  requires  all  forms  of  plant  food, 
it  may  be  said  that  nitrogen  and  potash  stimulate  the  growth  of 
leaves  and  stem,  and  phosphoric  acid  stimulates  ripening  of  the 
fruit.  An  excess  of  nitrogen  tends  towards  a  large  development 
of  leaf  and  late  maturity.  Thus  at  Rothamsted,  on  the  wheat 
plots  which  receive  nitrogen  and  potash  but  no  phosphoric  acid, 
the  grain  hardly  ripens  at  all.  The  use  of  phosphoric  acid,  how- 
ever, hastens  the  maturity  of  the  plant. 

Fertilizer  Experiments. — A  great  number  of  fertilizer  experi- 
ments have  been  carried  out  by  Experiment  Stations,  and  other 
investigating  agencies.  The  plans  of  the  experiments  vary  a  great 
deal,  according  to  the  crop  to  be  tested,  the  information  desired, 


326  PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

etc.  The  fertilizer  is  applied  to  plots  varying  from  1/50  to  1/2 
an  acre,  but  generally  of  T/IO  to  1/20  acre.  The  effect  of  the 
different  applications  is  measured  by  the  weight  of  the  product 
on  the  different  plots.  The  only  variable  should,  of  course,  be 
the  fertilizer.  All  other  conditions  should  be  the  same  for  all 
the  plots.  The  crop,  however,  is  subject  to  other  variables,  such 
as  differences  in  soil  or  subsoil,  in  stand,  damage  by  insect  pests, 
nearby  trees  or  fences,  etc.  The  best  results  are  secured  when 
the  experiment  is  carried  out  on  the  same  land  for  a  number  of 


A  B 

Fig-  75-  — Tobacco,  fertilized  (A),  and  unfertilized  (B).     Ohio  Station. 

years  to  eliminate  seasonal  differences.  It  is  also  well  for  plots 
to  be  repeated  a  number  of  times  in  order  to  eliminate  error  due 
to  inequalities  of  the  soil. 

In  order  to  study  the  effect  of  variable  soil  on  the  crop,  several 
experiments  have  been  made  in  which  a  field  of  apparently  uni- 
form soil,  bearing  a  crop  under  similar  conditions  in  all  parts,  has 
been  subdivided  and  harvested  in  separate  small  areas.  Com- 


PURCHASE:  AND  USE  OF  FERTILIZERS 


327 


parison  shows  the  differences  between  these,  and  combination  and 
comparison  shows  the  differences  of  larger  areas.  For  example, 
Morgan1  selected  a  strip  of  land  112^2  feet  wide  apparently  uni- 
form in  texture,  etc.,  which  was  planted  in  wheat  first  and  then 
corn.  It  was  measured  off  in  strips  15x112^  feet,  (about  1/25 
acre)  and  the  wheat  or  corn  harvested  separately  from  63  plots 
which  should  thus  be  all  alike.  With  the  average  yield  at  100, 
the  wheat  crop  varied  from  65.0  to  130,  and  the  corn  crop  from 

169.3  to  42.3. 

The  plot  yielding  the  lowest  with  wheat  gave  an  average  yield 
with  corn,  the  highest  with  wheat  88.5  with  corn.  The  plot  lowest 
with  corn  was  1 13.7  with  wheat,  and  the  plot  highest  with  corn  was 

100.4  with  wheat.     Thus  the  differences  were  not  in  the  same 
direction   with   the   two    successive   crops.     Assuming   that   the 
theoretical  yield  depended  upon  the  distance  from  the  check  plot, 
the  following  average  errors  were  found : 


Average 
error 

Wheat 

Average 
error 

Corn 

Per  cent. 

8.3 

8-4 
6.4 
5-6 

Per  cent. 

23.1 
15.7 
15-7 
ii.  3 

Assuming  different  treatments  for  the  plots,  the  average  and 
maximum  error  was  found  to  be  as  follows : 


Average  error 

Maximum  error 

Wheat 

Corn 

Wheat 

Corn 

Every  plot  different  treatment  .  .  '.  .  . 

Per  cent. 

12.4 
5-9 
5-8 
5-o 

Per  cent. 

31.7 
4-7 

3-2 

2-3 

Per  cent. 

64.0 
ii.  5 
7-6 
3-8 

Per  cent. 

I58.I 
15-7 

II.  0 

4-7 

Proc.  Am.  Soc.  Agri.,  1909.     See  also  Lyon,  ibid.,  1910,  p.  35-38. 


328  PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

This  experiment  shows  the  great  variation  in  the  produce  of 
two  crops  grown  under  apparently  the  same  conditions  in  a  field 
apparently  uniform.  It  also  shows  that  the  error  resulting  from 
variations  may  be  reduced  by  using  a  sufficient  number  of  check 
plots,  and  by  repeating  the  treatment  on  different  plots.  Great 
care  must,  therefore,  be  exercised  in  planning  and  conducting  field 
experiments. 

A  similar  experiment  is  reported  by  Smith  from  the  Illinois 
Experiment  Station,  on  120  one-tenth  acre  plots  of  corn  all  treated 
alike  for  three  years.  In  1895  the  yield  varied  from  11.4  to  50.2 
bushels  per  acre,  in  1896  from  48.5  to  103.9,  and  in  1897  from 
44.2  to  80.2  bushels.  The  lowest  yield  in  1897  was  on  the  plot 
which  gave  the  highest  yield  in  1896.  The  maximum  variation  in 
adjoining  plots  was  18  bushels  in  1895,  n  bushels  in  1896,  and  8 
bushels  in  1897. 

Precautions  in  Making  Fertilizer  Experiments. — The  following 
are  some  of  the  precautions1  to  be  used : 

(1)  The  greatest  care  should  be  taken  to  select  land  which  is 
as  uniform  as  possible  in  fertility.     Lack  of  uniformity  will  give 
misleading   results,   and  often   render  the  experiments   of  little 
value. 

(2)  Level  land  should  be  selected  if  possible.     If  such  cannot 
be  had,  the  plots  should  run  up  and  down  the  slopes,  so  that  the 
washing  by  rain  will  not  carry  fertilizing  materials  from  one  plot 
to  another. 

(3)  The  experimental  plots  should  be  measured  off  carefully, 
and  each  plot  indicated  by  stakes  or  stones. 

(4)  It  is  best  to  have  the  experimental  plots  long  and  narrow, 
because  thus  they  will  average  up  for  uneveness  of  soil. 

(5)  It  is  best  to  separate  plots  by  paths,  to  prevent  roots  of 
plants  in  one  plot  from  feeding  on  the  fertilizer  supplied  to  ad- 
joining plots. 

(6)  Avoid  windy  days  in  applying  fertilizers,  so  that  they  may 
not  be  blown  and  scattered  unevenly  over  the  plots. 

1  Thome,  Circular  96,  Ohio  Exp.  Sta. 


PURCHASE   AND   USE   OF   FERTILIZERS 


329 


(/)   All  the  plots  must  be  treated  alike  in  every  respect,  except 
as  to  the  amount  and  kind  of  fertilizer  applied.     The  same  kind 


Sect 

ion  A 

K            X            X            *               XXX 

XXX               X            X            x            X 

Sec 

ionB 

>:         x         x         x           xxx 

xxx          x        y        x        x 

Sec 

ionC 

X            X            X            X               XXX 

Sec 

ion  D 

x         x         x           x         x         x         X 

Fig.  76.— Plots  for  a  fertilizer  and  rotation  experiment,  four  sections  of  40 
plots  each.     The  plots  marked  (X)  are  check  plots.     Ohio  Station. 

and  quality  of  seed  must  be  used  over  the   entire  area.     The 
plowing  or  sowing  on  all  the  plots  must  be  done  the  same  day. 

22 


330 


PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 


If  part  of  the  crop  be  planted  before  and  part  after  a  rain,  the 
experiment  may  become  valueless.  Every  precaution  should  be 
used  to  secure  a  full  stand  of  plants,  and  if  a  uniform  stand  is 
not  secured  at  the  first  planting,  the  whole  field  should  be  re- 
planted. The  same  number  of  rows  should  be  arranged  on  each 
plot,  and  the  same  number  of  hills  and  plants  in  each  row,  as 
nearly  as  possible.  The  plots  should  be  plowed  and  cultivated 
alike,  and  whatever  operation  is  needed  on  one  experimental  plot 
should  be  carried  out  uniformly  on  all  the  plots. 

(8)  The  harvesting  of  the  crop  and  weighing  of  yields  must  be 
accurate.     A  small  mistake  is  multiplied  many  times  when  cal- 
culated to  an  acre. 

(9)  Provide  liberally  for  check  plots,  and  for  plots  on  which 
repetition  is  made,  so  as  to  allow  for  inequalities  of  the  soil. 

At  the  Rhode  Island  Station,1  the  plots  are  193.6  feet  long  by 
30  feet  wide,  with  3  foot  paths  between,  and  roads  at  the  end. 
Before  the  final  harvest,  the  crop  from  a  strip  of  land  three  feet 
wide  on  the  sides  and  six  feet  wide  at  the  ends,  is  cut  and  re- 
moved, this  leaving  exactly  one-tenth  acre  to  be  harvested.  This 
arrangement  eliminates  the  error  due  to  greater  growth  on  the 
edges  of  the  plot. 

The  importance  of  continuing  field  tests  several  years  is  shown 
by  Thome.-  The  results  from  the  first  year  test  on  wheat  is 
quite  different  from  the  ten  year  average : 


Addition 

Increase  +  and  decrease  — 
in  yield  of  wheat  in  bushels 
per  acre. 

First  year 
1894 

Average 

for  10  years 

bushels 
—2.8 

+5-6 

—  1.  21 

—4-7 

—  0.  4 

bushels 

+  6.5 
h   1-3 

h  1.8 
+  u  .4 
+  14.8 

Acid,  phosphate  and.  nitrate  soda.  

Acid  phosphate   potash  and  nitrate  

1  Report  for  1904. 

'2  Ohio  Circular  No.  96. 


PURCHASE   AND   USE   OF   FERTILIZERS 


33* 


He  also  shows  the  effect  of  the  fertilizer  to  increase  from  year 
to  year,  as  per  the  following  results  on  a  plot  receiving  a  complete 
fertilizer. 


Bushels  per  acre 

Corn 

Oats 

8-5 
II.  2 

15-2 

12.  1 

14-5 
18.0 

Thorne1  corrects  for  variations  in  the  soil  by  assuming  that 
variations  in  fertility  are  regular  from  one  check  to  the  next. 
The  difference  between  this  method  and  the  method  of  deducting 


If 


309* 


Pig,  77. — The  same  fertilizers  give  the  same  increase  if  the  land  decreases 

regularly  (CD)  from  the  checks,  but  not  if  the  average  of 

the  checks  (A  B)  is  deducted.     Ohio  Station. 

the  average  of  all  plots,  is  well  brought  out  in  Thome's  diagram. 
This  represents  four  plots  fertilized  alike  and  three  check  plots. 
The  increase  in  the  average  crop  is  regular  if  the  soil  varies  uni- 
formly, but  the  results  are  unconsistent  if  the  average  yield  of 
the  plots  are  deducted. 

1  Circular  96,  Ohio  Station. 


332 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Examples  of  Fertilizer  Experiments. — The  oldest  and  most 
famous  fertilizer  experiments  are  those  at  Rothamsted,  England. 
Other  important,  long  continued  field  experiments  are  those  of 
the  Ohio  Experiment  Station  at  Wooster,  the  Rhode  Island  Ex- 
periment Station,  at  Kingston,  the  Pennsylvania  Experiment 
Station  at  State  College,  and  the  North  Carolina  State  Board  of 
Agriculture  at  Statesville,  Red  Springs,  and  Edgecombe,  North 
Carolina. 


Fig.  78. — Experimental  plot  at  the  University  of  Nebraska. 

The  Rothamsted  experiments  were  begun  in  1848,  and  are  im- 
portant not  only  for  having  been  long  continued  under  the  same 
plan,  but  also  for  the  other  valuable  scientific  studies  made  there. 
The  Rhode  Island  Experiments  are  most  important  for  their  bear- 
ing upon  soil  acidity.  The  Ohio1  experiments  are  very  significant 
as  regards  rotation  and  manure. 

The  Rothamsted  experiments  comprise  seven  experimental 
fields:  (i)  crops  grown  in  rotation,  (2)  wheat  continuously 
1  Bulletins  uo,  182,  183  and  184.  Circular  120. 


PURCHASE   AND   USE   OF    FLvRTFUZKRS 


333 


grown,  (3)  wheat  alternating  with  fallow,  (4)  barley  continu- 
ously, (5)  potatoes  continuously,  (6)  hay  continuously,  (7)  ex- 
periments on  root  crops.  Most  of  the  plots  are  about  ^2  acre 
each.  The  plots  are  very  long  and  narrow  and  separated  by 
paths. 

The  following  is  part  of  the  plan  of  the  wheat  experiments  on 
Broadbalk  field1  with  some  of  the  results. 


Plot 


Application 


Average  bushels 

wheat,  51  years, 

1851-1962. 


9 

10 

ir 

12 
13 
H 
15 

16 

I? 
18 

19 


nitrogen    as    ammonium 

nitrogen    as    ammonium 

nitrogen   as  ammonim 


Manure,  14  tons 

Nothing 

Minerals2 

Minerals  and   43   pounds 

sulphate 

Minerals  and   86   pounds 

sulphate 

Minerals    and    129    pounds 

sulphate 

Minerals  and  43  pounds  nitrogen  as  nitrate  of  soda  - . 

86  pounds  nitrogen  as  ammonium  sulphate 

86  pounds  nitrogen  as  ammonium  sulphate. and  acid 

phosphate 

Same  as  n,  plus  sulphate  of  soda 

Same  as  n,  plus  sulphate  of  potash 

Same  as  1 1,  plus  sulphate  of  magnesia 

Mineral   plus    86    pounds    nitrogen    as    ammonium 

sulphate  ( applied  in  autumn ) 

Minerals  plus  86  pounds  nitrogen  in  nitrate  of  soda- . 
J  Minerals  alone  or  86  pounds  nitrogen  as  ammonium 

(      sulphate  alone  in  alternate  years 

92.6  pounds  nitrogen  in  rape  cake 


35-7 
13-1 
14-9 

24.0 
32.9 

37-i 

(27-3)3 

20.7 

24.0 
30.0 

3i-5 
30.1 

30.6 


40.  4 
(28.0)* 


Pennsylvania  Experiments6  at  State  College,  were  begun  in 
1882,  on  four  fields  of  144  plots  of  Y%  acre,  about  i1/^  rods  wide 
by  1 6  rods  long.  A  four-year  rotation  of  corn,  oats,  wheat,  and 
hay  of  mixed  clover  and  timothy  is  followed,  each  of  the  crops 

1  An  Account  of  the  Rothamsted  Experiments,  Hall. 

2  Minerals  consist  of  superphosphate,  with  sulphates  of   potash,  soda, 
and  magnesia. 

3  Average  for  10  years  only. 

4  Average  for  minerals. 

5  Average  for  nitrogen. 

6  Report  1910-11. 


334 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


being  grown  on  one  of  the  four  fields  every  year.  There  are  at 
least  four  plots  of  the  same  treatment,  one  in  each  field.  The 
fertilizer  is  applied  to  the  corn  and  wheat  only. 

Son,  TREATMENT  (PENNSYLVANIA). 


i-O 

i3-Plasler 

25-PK 

2-N 

14-0 

26-PNK(Na) 

3-P 

I5-PK 

27-PK2N(Na) 

4-K 

i6-Manure  12 

28-PK3N(Na) 

5-PN 

I7-PNK 

29-PK 

6-NK 

i8-Manure  16 

3o-PNK(S03) 

7-PK 

I9-PK2N 

3i-PK2N(SO3) 

8-Manure  (prior  to  1882) 

20-Manure  20 

32-PK3N(S03) 

9-PKN 

2I-PK3N 

33-Plaster 

10-PK2N 

22-CaO  Manure  12 

34-Limestone 

n-PNK(Bn) 

23-CaO 

35-PNK(Bn) 

I2-PNK 

24-0 

36-0 

N  stands  for  48  pounds  nitrogen,  2N  for  96  pounds,  3N  for  144 
pounds  per  acre.  Blood  was  used  in  the  first  24  plots,  except  No. 
n,  Nitrate  of  soda  in  plots  26-7-8  (marked  Na)  and  sulphate  of 
ammonia  in  plots  30-1-2  (marked  SO8).  K  signifies  160  pounds 
muriate  of  potash,  P  for  phosphoric  acid  in  dissolved  bone  black. 
Manure  was  used  at  the  rate  of  12,  16,  and  20  tons  per  acre. 
Plaster  is  640  pounds  land  plaster  (gypsum).  CaO  is  2  tons 
caustic  lime.  Limestone  is  4  tons  ground  limestone.  Blood  and 
bone  were  used  on  plots  1 1  and  35  for  nitrogen  and  phosphoric 
acid,  respectively. 

Comparative  Effects  of  Different  Plant  Foods. — In  comparing 
the  results  of  plot  experiments,  it  is  important  to  determine  the 
effect  of  the  individual  fertilizing  constituents,  namely,  of  phos- 
phoric acid,  nitrogen,  potash,  or  lime.  The  fertilizing  constituents 
exert  some  influence  upon  the  relative  action  of  each  other,  but 
nevertheless  it  is  often  advisable  to  estimate  the  value  of  each  in- 
dependently. This  can  be  done  by  subtracting  the  yield  without 
the  constituent  in  question  from  that  with  it.  Thus  the  yield  with 
phosphoric  acid,  potash,  and  nitrogen  less  that  with  phosphoric 
acid  and  potash  gives  the  effect  of  nitrogen;  by  subtracting  the 
yield  with  phosphoric  acid  and  nitrogen  we  get  the  effect  of 


PURCHASE   AND   USE   OF   FERTILIZERS 


335 


potash,  and  so  on.  Calculated  in  this  way,  the  following  table 
gives  the  increase  in  yield  of  ear  corn  produced  by  phosphoric 
acid,  potash,  and  nitrogen  respectively,  from  the  Wooster  Experi- 
ment Field  of  the  Ohio  Experiment  Station. 


Bushels  of  ear  corn  produced  by 

Phosphoric 
acid 

Potash 

Nitrogen 

6.6 

6.7 
9-2 

II.  O 

&4 

4.0 
4.2 

0.2 
2.1 

'    2.6 

3-9 

6.5 

o.o 

4-7 
3-8 

With  potash  

These  figures  show  the  effect  of  phosphoric  acid  or  potash  or 
nitrogen,  alone,  or  added  to  the  other  forms  of  plant  food.  On 
this  particular  soil  phosphoric  acid  had  the  greatest  effect,  nitro- 
gen next,  and  potash  least. 

Other  studies  and  applications  of  the  experiments  are  made, 
according  to  their  character. 

Value  of  Increase. — The  profit  in  the  use  of  different  fertilizing 
ingredients  depends  chiefly  on  the  cost  of  the  fertilizer  and  the 
market  value  of  the  product.  These  two  factors  vary  from  year  to 
}ear,  so  that  the  prices  used  must  always  be  given,  and  must  be 
carefully  compared  with  present  prices  in  studying  the  figures  at 
later  periods  of  time.  The  profit  can  be  calculated  by  subtract- 
ing the  cost  of  the  fertilizer  from  the  value  of  the  increase  in 
crop.  We  can  also  calculate  the  profit  or  loss  due  to  the  use  of 
specific  ingredients  of  the  fertilizer  as  explained  in  the  preceding 
section.  For  example,  the  following  results  were  secured  from 
seven  years  experiments  with  a  rotation  of  corn,  oats,  wheat,  and 
hay  on  the  Strongsville  Farm  of  the  Ohio  Experiment  Station.1 
1  Bulletin  184. 


336 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Total  profit  (  +  ),  or  loss  (  —  ) 
per  acre  from  the  use  of 

Phosphoric 
acid 

Potash 

Nitrogen 

+  I2.I6 

+  11.42 

+  13-79 
+  15.08 

—5-97 
-6.7I 

—4-57 
-3-28 

—11-43 
—  9.80 
—  10.03 

-    6.37 

With  potash  

^^ith  nitrogen  •  

+  I3-11 

—5  14 

-  9-41 

On  this  particular  soil,  with  the  amounts  of  fertilizers  used  and 
crops  grown  and  at  the  prices  given,  phosphoric  acid  alone  was 
profitable,  potash  and  nitrogen  being  applied  at  a  loss  in  both 
cases.  On  other  soils  and  with  other  crops,  different  results 
would  be  secured.  These  figures  are  merely  given  to  show  the 
method  of  calculating.  Additional  expense  due  to  handling  the 
increased  crop,  and  the  fertilizer,  should  also  be  considered. 

Systems  of  Fertilization. — There  is  a  great  diversity  in  soils, 
crops,  climatic  conditions,  and  other  factors  which  modify  the 
effect  of  fertilizers.  Individuals  must  study  their  own  condi- 
tions, try  various  combinations,  and  use  such  mixtures  as  give 
most  profitable  results  under  their  conditions.  Fertilizers  which 
give  good  results  are  recommended  in  the  various  publications  on 
the  subject,  but  the  application  which  will  be  the  best  and  the 
most  profitable  will  depend  upon  individual  conditions. 

Systematic  use  of  fertilizers  is  more  profitable  than  haphazard. 
The  following  are  some  of  the  systems1  which  are  used.  Every 
system  should  include  a  rotation  of  crops,  with  liberal  use  of 
manure  or  green  crops  plowed  under. 

i.  System  Based  on  Influence  of  a  Single  Element. — This 
system  assumes  that  plants  can  be  divided  into  three  groups ;  one 
group  most  benefited  by  nitrogenous  fertilizers,  another  by  phos- 
phatic,  and  the  third  by  potassic.  Nitrogen  is  said  to  be  the 
dominant  element  for  wheat,  rye,  oats,  barley,  meadow  grass,  and 
beet  crops.  Phosphoric  acid  is  dominant  for  Indian  corn,  sorg- 
1  Voorhees'  Fertilizers. 


PURCHASE   AND   USE  OF   FERTILIZERS  337 

hum,  sugar  cane,  turnips,  and  Swedes.  Potash  is  the  ruling 
ingredient  for  peas,  beans,  clover,  vetch,  flax,  and  potatoes.  If 
the  soil  is  fertile,  the  dominant  element  would  be  supplied  to 
force  a  maximum  growth  of  the  crop,  in  such  quantity  as  might 
be  found  necessary.  If  the  soil  is  not  fertile,  moderate  applica- 
tions of  the  other  plant  foods  are  made,  supplemented  with  more 
liberal  additions  of  the  dominant  element. 

2.  System  Based  on  Necessity  of  an  Abundant  Supply  of  the 
Minerals. — This  system  is  based  upon  the  fact  that  potash  and 
phosphoric  acid  are  cheap  and  not  easily  washed  from  the  soil, 
while  nitrogen  is  expensive  and  easily  lost.     According  to  the 
needs  of  the  soil,  a  reasonable  excess  of  phosphoric  acid  and 
potash  is  applied,  sufficient  to  satisfy  more  than  the  maximum 
needs  of  any  crop,  and  then  the  nitrogen  is  applied  in  active 
forms,  such  as  nitrate  of  soda  or  sulphate  of  ammonia,  and  at 
such   times   as  will   insure  the   minimum  loss   of   nitrogen   and 
the  maximum  development  of  the  plant.     The  phosphoric  acid 
may  be   drawn   from  the  cheaper  mineral   substances,   such   as 
ground  bone,  tankage,  and  ground  phosphate  rock. 

This  system  is  useful  in  building  up  a  very  poor  soil  when  ac- 
companied by  a  rotation  which  involves  the  use  of  legumes  and 
manure. 

3.  A  System  Based  on  the  Amount  of  Plant  Food  Taken  up  by 
the  Crop. — According  to  this  system,  different  plants  are  fertilized 
with  phosphoric  acid,  nitrogen,  and  potash  in  the  proportions  in 
which  chemical  analysis  shows  them  to  exist  in  the  plants.     If 
care  is  taken  to  supply  an  abundance  of  plant  food,  this  method 
may  result  in  complete,  though  not  economical,  feeding  of  the 
plant,  and  may  be  profitable  for  crops  of  high  value  per  acre,  but 
for  ordinary  farm  crops,  it  is  likely  to  be  unprofitable. 

This  system  does  not  take  into  consideration  the  fact  that  one 
plant  may  have  much  greater  power  of  taking  up  an  element  than 
another.  Neither  does  it  consider  that  the  period  or  season  of 
growth  exercises  some  effect  on  the  capability  of  a  plant  to  ac- 
quire plant  food  from  the  soil.  It  may,  however,  be  taken  as  a 
general  rule  that  an  application  of  easily  available  plant  food 


PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

largely  in  excess  of  the  requirements  of  the  crop,  is  not  advisable. 
Such  an  application  is  likely  to  lead  to  loss  of  plant  food,  either 
by  percolation  or  by  fixation. 

4.  The  Fertilizer  is  Applied  to  the  Money  Crop  in  a  Rotation. — 
In  this  system,  the  money  crop  is  supplied  with  an  abundance  of 
plant  food,  so  as  to  insure  continuous  feeding  and  maximum  pro- 
duction. The  remaining  crops,  or  those  immediately  succeeding 
in  the  rotation,  are  nourished  by  the  residues,  with  small  applica- 
tions of  fertilizer,  if  necessary.  If,  for  example,  the  rotation  is 
cotton,  corn,  and  cowpeas,  the  cotton  would  be  liberally  fertilized, 
the  corn  and  cowpeas  being  allowed  to  feed  on  the  residues. 

Use  of  Nitrate  of  Soda. — Nitrate  of  soda  is  easily  soluble  in 
water,  and  distributes  itself  through  the  soil,  and  as  the  nitrogen 
can  be  easily  taken  up  by  plants,  it  is  quickly  effective.  On  the 
other  hand,  it  is  so  soluble  in  water  that  it  is  easily  washed  from 
the  soil  by  rains,  and  there  may  be  loss  from  leaching  when 
applied  previous  to  the  growth  of  the  plant,  or  in  too  large 
quantities  at  the  wrong  time,  or  when  heavy  rains  occur  im- 
mediately after  its  application. 

The  best  use  of  nitrate  of  soda1  is  secured  when  an  abundant 
supply  of  potash  and  phosphoric  acid  is  present.  We  have  al- 
ready seen  that  the  size  of  a  crop  is  controlled  by  the  most  un- 
favorable condition,  and  if  potash  or  phosphoric  acid  are  deficient, 
this  deficiency  cannot  be  overcome  by  the  use  of  nitrate  of  soda. 

The  best  use  of  nitrate  of  soda  is  also  secured  when  it  is  applied 
to  soils  in  good  condition  rather  than  to  poor  or  worn  out  soils. 
Larger  quantities  may  profitably  be  applied  to  good  soils  than  to 
poor  soils.  Clods  and  lumps  prevent  a  proper  distribution  of  the 
material  as  well  as  a  ready  absorption  of  plant  food,  which  are 
also  necessary  for  good  results.  The  application  of  nitrate  of 
soda  is  especially  advantageous  for  quick  growing  vegetable  crops, 
where  market  quality  is  measured  by  rapid  and  continuous 
growth,  and  for  those  field  crops  which  make  their  greatest 
development  in  spring,  before  the  conditions  are  favorable  for  the 
change  of  the  nitrogen  in  the  soil  into  forms  usable  by  plants. 
1  Bulletin  172,  New  Jersey  Station. 


PURCHASE  AND   USE   OF   FERTILIZERS  339 

Apply  100  pounds  per  acre  on  poor  soils,  150  pounds  on  good 
soils,  as  a  top  dressing  in  the  spring  after  the  grass  or  crop  is  well 
started.  For  ordinary  field  crops,  since  nitrogen  is  so  expensive, 
the  increase  in  yield  may  not  pay  for  nitrogen  used  in  fertilizer. 

Crops  grown  in  the  early  spring,  such  as  early  spring  forage, 
or  spring  wheat,  oats,  etc.,  may  be  unable  to  secure  sufficient  nitro- 
gen from  the  soil  to  permit  of  rapid  and  maximum  development. 

The  agencies  which  change  organic  into  active  nitrogen  may 
not  be  sufficiently  active  to  produce  a  sufficient  supply  of  active 
nitrogen.  Hence  an  application  of  active  nitrogen  in  the  form  of 
nitrate  of  soda  may  cause  great  gains  to  take  place.  Some  crops, 
as  tomatoes,  cabbage,  potatoes,  etc.,  must  be  grown  and  harvested 
early,  in  order  to  be  highly  profitable.  Hence  their  growth  must 
be  forced  at  a  time  when  the  natural  agencies  are  not  very  active. 

According  to  bulletins  of  the  New  Jersey  Experiment  Station, 
the  use  of  150  pounds  per  acre  of  nitrate  of  soda  has  increased  the 
wheat  crop  9  bushels  per  acre.  Early  tomatoes  were  increased  in 
value  50  per  cent,  by  150  to  250  pounds,  early  cabbage  40  to  80 
per  cent,  by  400  pounds,  musk  melons  doubled  in  value  by  200 
pounds. 

Quantity  of  Fertilizer. — The  applications  of  different  quanti- 
ties of  the  same  fertilizer  follows  the  law  of  diminishing  returns. 
That  is,  the  increase  produced  by  each  successive  increment  of  fer- 
tilizer diminishes  as  the  quantity  of  fertilizer  increases.  Thus  the 
cost  of  the  increment  increases  with  the  quantity  of  fertilizer. 
The  fertilizer  is  profitable  up  to  a  certain  point,  after  which  the 
value  of  the  increase  is  not  equal  to  the  cost  of  the  additional 
amount  of  fertilizer.  The  most  profitable  quantity  depends  upon 
the  character  of  the  soil,  the  kind  of  crop  and  its  value,  and 
climatic  conditions.  The  more  valuable  the  crop,  the  larger  the 
quantity  of  fertilizer  which  may  be  profitable. 

As  an  illustration,  we  will  cite  the  experiments  conducted  for 

four  years  by  the  New  York  (Geneva)  Experiment  Station1  to 

ascertain  the  most  profitable  quantity  of  fertilizer  for  potatoes. 

The  fertilizer  used  contained  8  per  cent,  available  phosphoric  acid, 

1  Bulletin  187. 


340 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


4  per  cent,  nitrogen,  and  10  per  cent,  potash,  costing  $25.00  per 
ton.     The  average  of  the  four  crops  is  as  follows : 


Pounds  fertilizer  per  acre 

Increase 
in  fertilizer 

Increase  in  yield 
due  to  increase  in 
fertilizer 

Cost  of  fertilizer 
for  each  additional 
bushel  potatoes 

Bushels 

CQO 

2"?    -I 

$0  27 

3W"   • 

^uu 
cr)O 

^6-6 
2O  Q 

CQO 

^vj.y 
112 

o  ^6 

CQO 

6  0 

I    Od. 

The  first  500  pounds  fertilizer  produced  an  increase  of  23.3 
bushels  potatoes,  a  cost  of  27  cents  per  bushel  for  fertilizer.  The 
last  500  pounds  produced  6.0  bushels  at  a  cost  of  $1.04  per  bushel 
for. the  fertilizer. 

Secondary  Actions  of  Fertilizers. — The  supplying  of  available 
plant  food  is  the  primary  action  of  fertilizers.  They  have  other 
secondary  actions  upon  the  soil,  which  may  not  be  unimportant  at 
times. 

Reaction. — Sulphate  of  ammonia  leaves  an  acid  residue  in  the 
soil,  which  unites  with  lime,  increases  the  loss  of  lime,  and  may 
cause  a  soil  not  rich  in  lime  to  become  acid.  This  has  taken 
place  at  the  Woburn  (England)  Experiment-  Farm,  where  the 
plot  which  receives  sulphate  of  ammonia  has  become  acid  and  will 
not  grow  barley.  Addition  of  lime  corrects  the  acidity. 

Acid  phosphate  may  also  have  a  slight  tendency  towards  caus- 
ing soil  acidity.  Nitrate  of  soda  leaves  a  basic  residue  in  the  soil, 
and  hence  has  a  tendency  to  correct  acidity.  Organic  nitrogenous 
fertilizers  do  not  affect  the  reaction  of  the  soil. 

Physical  Structure. — Acid  phosphate  tends  to  flocculate  a  clay 
soil.  Nitrate  of  soda  tends  to  cause  it  to  puddle  or  run  together. 
Potash  salts  vary  somewhat  in  their  action,  according  to  the 
nature  of  the  soil. 

Fertilisers  Conserve  Moisture. — Fertilizers  may  decrease  trans- 
piration and  reduce  the  quantity  of  water  required  to  produce 
growth.  For  example,  Widstoe  reports  the  quantity  of  water 


PURCHASE:  AND  USE  OF  FERTILIZERS  341 

transpired  per  i  gram  dry  matter  produced  in  one  experiment  on 
corn  in  pots  as  follows : 

Grams 

No  fertilizer 1,012 

Phosphates 735 

Nitrates 555 

Phosphate  and  nitrate 1 78 

Bacterial  action  is  undoubtedly  affected  by  fertilizers,  but  to 
what  extent  or  of  what  importance  is  not  known. 

It  is  claimed  that  the  sulphate  of  lime  which  is  present  in  acid 
phosphate  may  liberate  soil  potash  and  so  render  it  available  to 
plants.  It  is  also  possible  that  this  sulphate  of  lime  may  supply 
plants  directly  with  sulphur,  but  this  is  a  matter  which  requires 
further  study. 

Whitney  claims  that  fertilizers  destroy  toxic  substances  in  the 
soil,  but  no  direct  evidence  has  been  brought  forward  to  show 
that  such  is  the  case. 

Relation  of  Fertilizers  to  Losses  and  Changes  of  Plant  Food.— 
When  nitrogen,  and,  to  a  less  extent,  potash,  is  added  to  the  soil, 
the  loss  due  to  percolation  increases.  This  is  shown  by  analyses 
of  percolation  waters  from  drain  gauges  or  tile  drains.  See 
Chapter  XIII.  There  is  also  an  increased  los;  due  to  denitri- 
fication,  which  can  be  ascertained  by  analysis  of  the  soil  after  a 
number  of  years,  provided  loss  by  percolation  and  cropping  is 
also  known.  Little  loss  of  phosphoric  acid  takes  place,  except 
possibly  on  very  light  sandy  soils. 

Fertilizers  improperly  used  may  diminish  the  fertility  of  the 
soil.  Thus  acid  phosphate  alone  will  give  good  results  on  some 
soils  for  a  few  years,  but  the  increased  crop  increases  the  draft 
upon  the  nitrogen  and  potash  of  the  soil.  Unless  provision  is 
made  to  restore  the  loss  of  nitrogen  and  potash,  the  acid  phos- 
phate will  become  less  and  less  effective.  The  same  is  true, 
though  to  a  less  extent,  of  fertilizers  containing  large  percentages 
of  phosphoric  acid  and  small  percentages  of  nitrogen  and  potash, 
such  as  a  fertilizer  containing  8  or  10  per  cent,  available  phos- 
phoric acid,  2  per  cent,  nitrogen,  and  2  per  cent,  potash,  such  as 
are  commonly  used  in  the  South  for  fertilizing  cotton  and  corn. 


342  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Used  in  small  quantities,  these  fertilizers  tend  to  deplete  the  soil 
of  nitrogen,  unless  provision  is  made  to  restore  it  otherwise.  The 
use  of  such  fertilizers  in  large  quantity  is  not  to  be  recommended, 
since  a  great  deal  more  phosphoric  acid  is  supplied  than  can 
possibly  be  utilized  by  the  crop.  If  more  fertilizer  is  used,  it 
should  be  richer  in  nitrogen. 

Effect  of  Fertilizer  on  Succeeding  Crops. — The  effect  of  fer- 
tilizer carried  over  to  a  subsequent  year  is  shown  in  the  experi- 
ments at  Rothamsted.  Plot  17  and  18  receive  "mineral  manure" 
consisting  of  superphosphate  and  sulphates  of  potash,  soda,  and 
magnesia  one  year,  and  86  pounds  nitrogen  in  sulphate  of  am- 
monia the  second  year.  These  applications  have  alternated  for 
51  years.  The  average  results  are  as  follows: 

Bushels  of  wheat 
per  acre 

Plot  5  —mineral  manure " 14.9 

(A)  Plots  17-18  when  mineral  manure  etc.,  is  applied 15.3 

(B)  Plots  17-18  when  sulphate  of  ammonia  is  applied 30.4 

Plot  7 — complete  fertilizer    32.9 

Thus  plots  17-18  produce  little  more  crops  the  year  after  the 
application  of  sulphate  of  ammonia  (A)  than  plot  5  which  re- 
ceives no  ammonia.  Plots  17-18  produce  nearly  as  much  the 
year  after  the  application  of  the  phosphoric  acid  and  potash,  as 
they  do  in  plot  7  which  receives  them  every  year.  That  is  to  say, 
the  phosphoric  acid  and  potash  remain  in  the  soil  in  an  available 
form,  so  as  to  be  useful  to  the  next  crop,  while  the  nitrogen  was 
leached  out  or  otherwise  rendered  of  little  value  to  the  plant. 

Fixation. — It  is  commonly  supposed  that  phosphoric  acid  and 
potash  of  fertilizers  are  fixed  and  rendered  less  soluble  almost  as 
soon  as  they  are  placed  in  the  soil.  This  is  not,  however,  the 
case.  Some  of  the  lumps  of  fertilizer  are  '%  inch  in  diameter, 
and  do  not  dissolve  at  once.  When  they  do  dissolve, 
diffusion  is  not  a  rapid  process,  and  the  soil  particles 
nearest  the  fertilizer  are  brought  in  contact  with  the  more  con- 
centrated solution,  and  fix  larger  proportions  of  it,  than  those 
farther  away.  Hence  the  fertilizer  becomes  the  center  of  a  zone 
of  concentrated  plant  food,  more  dilute  towards  the  outside.  This 


PURCHASE   AND   USE   OF   FERTILIZERS  343 

is  even  to  some  extent  true  of  the  easily  soluble  fertilizers,  like 
nitrate  of  soda,  for  which  the  soil  has  little  power  of  fixation,  but 
still  more  so  for  the  less  soluble  acid  phosphates.  In  the  case  of 
organic  nitrogenous  materials,  the  particles  become  centers  for 
the  production  of  ammonia  and  nitrates,  which  may  eventually  be 
taken  up  by  the  rootlets  as  fast  as  they  are  formed.  The  well 
known  fact  that  moderate  applications  of  fertilizer  are  more 
effective  when  applied  in  the  vicinity  of  the  plant  or  seed  than 
when  applied  broadcast,  is  evidence  that  the  plant  food  does  not 
become  rapidly  and  uniformly  distributed  through  the  soil  mass. 

The  Practice  of  Fertilization.1 — There  is  such  a  variation  in  the 
needs  of  crops  and  soils  for  fertilizers,  in  the  effect  of  climatic 
conditions,  and  previous  treatment,  upon  their  behavior  towards 
fertilizers,  that  it  is  impossible  to  lay  down  specific  rules  for  fer- 
tilization. The  fertilizer  which  produces  heavy  yields  of  potatoes 
in  the  North,  would  not  necessarily  be  suitable  for  the  warmer 
climate,  lighter  yields,  and  earliness,  associated  with  the  same 
crop  in  the  South.  Onions  grown  on  the  sandy  soils  of  Long 
Island,  New  York,  require  different  treatment  from  those  grown 
in  the  warmer  climate  and  much  richer  soils  under  irrigation  at 
Laredo,  Texas.  Applications  suited  to  crops  grown  under  favor- 
able conditions  of  moisture  may  be  unsuited  to  crops  which  may 
have  to  endure  a  period  of  drouth  or  mature  on  a  moderate 
amount  of  moisture.  The  best  that  can  be  done  is  to  lay  down 
general  principles,  and  to  give  the  applications  which  have  proved 
successful  under  certain  stated  conditions.  The  individual  farmer 
must  study  his  own  conditions,  with  the  help  of  his  State  Experi- 
ment Station,  and  learn  by  his  own  experience  the  most  profitable 
applications  for  him  to  make.  A  few  brief  notes  are  made  below 
on  fertilizers  for  various  crops. 

Field  Crops. — Rotation  of  crops,  including  legumes,  to  be 
turned  under  or  fed  and  the  manure  saved,  is  essential  to  mainten- 
ance of  fertility  for  ordinary  field  crops.  Only  in  this  way  can 
nitrogen  be  secured  cheap  enough.  Phosphates  and  potash  may 
1  See  Voorhees,  Fertilizers  ;  Van  Slyke,  Soils  and  Fertilizers  ;  Bulletins 
of  Bureau  of  Soils  and  of  State  Experiment  Stations. 


344  PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

be  purchased  as  necessary,  together  with  supplementary  small 
amounts  of  nitrogen.  Field  crops,  especially  grasses  and  clovers, 
utilize  insoluble  phosphates  fairly  well. 

Corn. — A  suitable  rotation,  including  careful  saving  of  all 
manure,  together  with  the  use  of  phosphoric  acid,  will  maintain 
corn  lands  at  a  good  level  of  productiveness,  or  increase  the  yields. 
The  phosphoric  acid  may  be  supplied  in  200  pounds  per  acre  of 
acid  phosphate  applied  annually,  or  2,000  pounds  of  rock  phos- 
phate applied  every  five  or  six  years.  An  application  of  nitrogen, 
such  as  contained  in  200  pounds  cottonseed  meal,  may  also  be 
effective.  Potash  is  needed  on  some  soils.  The  ordinary  corn 
and  cotton  fertilizer  used  in  the  South  contains  8  to  10  per  cent, 
available  phosphoric  acid,  1.65  to  2.5  per  cent,  nitrogen,  and  I  to 
3  per  cent,  potash.  It  is  used  at  the  rate  of  100  to  400  pounds 
per  acre. 

Oats. — Oats  in  a  rotation  often  receive  benefit  from  100  pounds 
acid  phosphate  applied  at  the  time  of  planting,  and  a  top  dressing 
of  100  pounds  nitrate  of  soda  when  the  plants  begin  their  vigorous 
spring  growth. 

Wheat. — Same  as  oats.  Clover  uses  much  potash  and  is  often 
benefited  by  100  pounds  acid  phosphate  and  50  pounds  muriate  of 
potash  per  acre.  Timothy  may  receive  the  same  application  as 
clover  and  in  addition  a  top  dressing  of  100  pounds  nitrate  of 
soda  in  the  spring.  Alfalfa  requires  lime  and  draws  heavily  on 
the  potash  of  the  soil.  A  good  application  is  200  pounds  acid 
phosphate,  20  pounds  nitrate  of  soda,  and  100  pounds  muriate  of 
potash  applied  just  before  planting.  This  may  be  supplemented 
by  300  pounds  acid  phosphate  and  200  pounds  muriate  of  potash 
per  acre  per  year.  Peanuts  are  similar  to  alfalfa.  A  great  deal 
depends  on  the  soil. 

Cotton. — Acid  phosphate  is  used  at  the  rate  of  100  to  200 
pounds  per  acre  on  land  which  produces  a  good  stalk  but  does 
not  fruit  well.  An  application  of  200  to  400  pounds  cottonseed 
meal  gives  good  results  on  many  soils.  The  Georgia  Experiment 
Station  recommends  for  old  worn  uplands,  a  mixture  of  1,000 
pounds  acid  phosphate,  671  pounds  cottonseed  meal,  and  296 


PURCHASE  AND  USD;  OF  FERTILIZERS  345 

pounds  kainit  applied  at  the  rate  of  400  to  800  pounds  per  acre. 
This  fertilizer  would  contain  8  per  cent,  phosphoric  acid,  2.4  per 
cent,  nitrogen,  and  2.4  per  cent,  potash.  A  rotation  of  crops  in- 
cluding legumes  should  be  adopted. 

Truck  Crops. — Rotation,  manure,  and  heavy  applications  of 
fertilizers  are  used  for  truck  crops. 

Potatoes  in  New  York  receive  1,000  to  2,000  pounds  of  a  fer- 
tilizer containing  about  8  per  cent,  available  phosphoric  acid,  4  per 
cent,  nitrogen,  and  10  per  cent,  potash.  In  Texas  good  results 
are  secured  with  a  mixture  of  800  pounds  acid  phosphate  and 
1,200  pounds  cottonseed  meal  at  the  rate  of  300  to  600  pounds 
per  acre.  Sweet  potatoes  in  New  Jersey  receive  500  to  700 
pounds  of  a  fertilizer  containing  3  per  cent,  nitrogen,  7  per  cent, 
available  phosphoric  acid,  12  per  cent,  potash.  In  Georgia,  200 
to  400  bushels  per  acre,  according  to  soil  and  season,  are  secured 
with  a  mixture  of  320  pounds  acid  phosphate,  360  pounds  cotton- 
seed meal,  and  640  pounds  kainit.  Early  tomatoes  in  New  Jersey 
receive  about  350  pounds  acid  phosphate  and  200  pounds  muriate 
of  potash  just  before  planting,  a  top  dressing  of'  100  pounds 
nitrate  of  soda  at  time  of  setting  out,  and  100  pounds  again  three 
or  four  weeks  later.  Onions  in  New  Jersey,  do  well  on  1,000 
pounds  of  a  fertilizer  containing  5  per  cent,  nitrogen,  6  per  cent, 
available  phosphoric  acid,  and  10  per  cent,  potash.  In  Texas, 
they  do  well  on  1,500  pounds  cottonseed  meal,  or  1,000  pounds  of 
a  fertilizer  containing  5  per  cent,  available  phosphoric  acid,  5  per 
cent,  nitrogen,  and  5  per  cent,  potash.  Cabbage  may  receive  an 
application  of  1,000  pounds  of  a  fertilizer  containing  4  per  cent, 
nitrogen,  8  per  cent,  phosphoric  acid,  and  5  per  cent,  potash, 
supplemented  by  a  top  dressing  of  100  pounds  nitrate  of  soda  and 
100  pounds  acid  phosphate  after  the  plants  begin  to  grow  when  set 
out,  and  100  pounds  when  the  heads  begin  to  form. 


CHAPTER  XVII. 


CONSTITUENTS  OF  PLANTS. 

For  the  purpose  of  ordinary  agricultural  analysis,  the  various 
compounds  in  plants  and  feeds  are  divided  into  six  groups,  each  of 
which,  with  the  exception  of  the  first  (water),  is  composed  of  a 
number  of  chemical  compounds,  varying  in  their  nature  and  rela- 
tive proportion  according  to  the  plant,  or  portion  of  plant,  under 
examination. 

These  groups  are  as  follows : 

1 i )  Water,  which  is  present  in  all  feeds. 

(2)  Ether  Extract. — This  is  the  material  extracted  by  ether 
and,  in  the  case  of  seeds,  is  composed  mostly  of  fats  and  oils,  but 
it  contains  large  quantities  of  substances  other  than  fats  in  the 
case  of  hays,  straw,  and  grass. 

(3)  Protein. — This  includes  all  the  nitrogenous  constituents  of 
the  plant  or  feed. 

(4)  Crude  Fiber. — This    is    the   residue   left   on   boiling   the 
material   with   sulphuric   acid   and   with   caustic   soda,   a   purely 
arbitrary    method.     It   consists   of    cellulose,    lignin,    cutin,    and 
other  substances. 

(5)  Ash. — This  is  the  residue  left  after  the  material  has  been 
burned,  and  consists  of  the  substances  not  volatile  at  the  tem- 
perature of  the  combustion.     It  consists  chiefly  of  lime,  magnesia, 
soda,  and  potash  united  with  phosphoric  acid,  chlorine,  carbon 
dioxide,  sulphur  trioxide,  silica,  and  some  unburned  carbon. 

(6)  Nitrogen-Free  Extract  comprises  all  the  other  ingredients 
of  the  plants  not  included  in  the  above  groups.     In  estimating 
its  quantity,  the  water,  protein,  ether-extract,  crude  fiber,  and 
ash,  are  added  together,  and  the  sum  subtracted  from  100.     The 
difference  is  the  nitrogen-free  extract. 

Water. — Water  is  abundantly  found  in  the  green  and  growing 
portions  of  the  plant,  as  in  leaves,  tender  shoots,  and  immature 
seeds,  but  chiefly  in  the  sap,  in  which  it  transports  the  materials 
used  in  the  growth  of  the  plants.  The  older  portions  of  plants, 
such  as  the  stems,  and  old  wood,  and  the  mature  seeds,  contain 


CONSTITUENTS  OF  PLANTS 


347 


smaller  percentages  of  water.  Substances  such  as  hays,  meals, 
etc.,  which  are  apparently  dry,  contain  appreciable  quantities  of 
water. 

The  following  table  shows  the  percentages  of  water  in  some  of 
the  different  classes  of  substances : 

WATER  IN  PLANTS. 


Green  plants 

Per  cent. 

Mature  seeds  and  hays 

Per  cent. 

Corn  leaves  

7Q  1 

Corn  fodder  ...   • 

42   2 

Timothv  

/V'O 

61  6 

Ximothv  hay  

4*  * 

Red  clover  

70  8 

Red  clover  hay  

1o-^ 

T  r    i 

81  6 

Cowpea  hay  

*5-3 
60  7 

78  Q 

T/1    8 

/o-v 
86  e; 

OUO 
QO   ^ 

Wheat  (seed)    - 

1U.^ 

yj-o 

7c    A 

1U.^ 

/J-Q 

Determination  of  Water. — The  usual  method  is  to  dry  the  sub- 
stance at  the  temperature  of  boiling  water  until  it  no  longer  loses 
weight  (about  five  hours).  The  operation  is  conducted  in  a 
water-oven.  This  consists  of  a  double  walled  box.  The  space 
between  inner  and  outer  walls  is  partly  filled  with  water,  and  the 
inner  chamber  is  heated  by  the  steam.  There  are  certain  sources 
of  error  in  the  estimation  of  moisture  which  must  be  guarded 
against,  some  of  which  are  as  follows : 

(1)  Absorption    of    Oxygen. — Certain    fats    and    oils    absorb 
oxygen  when  heated  in  the  air,  thus  gaining  in  weight ;  they  may 
also  become  insoluble  in  ether.     For  instance,  linseed  oil,  which 
occurs  in  linseed  meal,  absorbs  oxygen  with  avidity.     If  materials 
containing  such  oils  are  dried  in  the  air,  the  results  on  moisture 
are  too  low,  and  the  ether  extract  is  liable  to  be  too  low  also.  The 
remedy  is  to  dry  in  a  current  of  hydrogen,  or  of  illuminating  gas 
which  contains  no  oxygen.     Gasolene  gas  is  not  suitable. 

(2)  Chemical  Changes. — At  the  temperature  of  boiling  water, 
some  compounds  found  in  plants  may  undergo  chemical  change. 
The  sugar  in  ripe  fruits  may  be  decomposed,  or  caramelized.  For 
example,  Snyder1  found  fresh  tomatoes  to  contain  3.88  per  cent. 

1  Bulletin  13,  Minnesota  Station. 


348  PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 

sugar,  while  after  drying  at  100°  C.  only  2.04  per  cent,  was  pres- 
ent, a  loss  of  nearly  50  per  cent.,  due  to  decomposition.  The  de- 
composition may  produce  volatile  bodies,  and  thus  give  too  high 
results  for  water. 

Such  materials  should  be  dried  in  a  vacuum,  either  at  the 
ordinary  temperature,  or  at  a  slightly  elevated  temperature.  The 
drying  may  take  place  in  a  desiccator  which  contains  sulphuric 
acid  and  has  been  exhausted  with  a  vacuum  pump. 

(3)  Volatile  Materials. — Some  substances  lose  volatile  organic 
matter  when  dried  at  100°  in  a  current  of  air,  or  hydrogen. 

Silage  loses  acetic  acid  and  ammonium  acetate.  Tobacco  loses 
moisture.  Atwater  found  that  meats  and  fish  in  drying  lost  I 
to  4  per  cent,  of  their  total  nitrogenous  material.  Animal  excre- 
ments, both  liquid  and  solid,  may  lose  nitrogen. 

These  losses  may  in  some  instances  be  avoided  by  drying  in  a 
vacuum.  In  others  (as  with  urine  and  manure)  analyses*  should 
be  made  on  the  fresh  materials,  and  correction  made  for  the  loss. 

Ether  Extract. — The  mixture  of  substances  which  is  removed 
from  a  plant  by  extraction  with  ether  is  termed  ether  extract.  It 
is  often  termed  "fats  and  oils"  and  this  expression  is  correct  when 
reference  to  concentrated  feeding  stuffs  is  intended,  as  in  such 
cases  the  ether  extract  is  composed  mostly  of  fats  and  oils.  But 
when  applied  to  hays  or  fodders,  the  term  "fats  and  oils"  is  not 
correct,  since  the  ether  extract  may  contain  30  to  70  per  cent,  of 
substances  which  are  not  fats  or  oils,  such  as  chlorophyll,  hydro- 
carbons, and  wax  alcohols. 

Ether  extract  is  obtained  from  all  plants,  and  nearly  all  parts  of 
all  plants.  It  is  found  in  small  quantities  only,  in  roots  and  tubers, 
in  somewhat  larger  quantities  in  hays,  and  straws,  and  in  com- 
paratively large  quantities  in  certain  seeds,  such  as  the -seeds  of 
cotton,  flax,  peanut,  soja  bean,  almond,  and  sunflower.  These  are 
called  oil-bearing  seeds.  Certain  fruits,  such  as  the  olive,  are  also 
rich  in  oil. 

The  ether  extract  of  seeds  may  not  be  distributed  uniformly, 
but  may  be  concentrated  in  certain  parts  of  the  seed.  Thus, 
while  the  entire  grain  of  corn  contains  5.5  per  cent,  of  oil,  the 


CONSTITUENTS  OF  PLANTS 


349 


germ  contains  about  27  per  cent,  oil,  which  may  be  expressed 
from  it  for  commercial  purposes.  The  ether  extract  of  rye  and 
wheat  passes  mostly  into  the  bran  along  with  the  germ. 

The  percentage  of  ether  extract  in  some  of  the  different  classes 
of  materials  is  shown  in  the  following  table : 
ETHER  EXTRACT  IN  PLANTS. 


Per  cent. 

Per  cent. 

Beets 

o  I 

5c 

Potatoes  

O  I 

•O 
I  A. 

i  6 

Sola  bean  

16  Q 

Xitnottiy  hav  

•J    7 

Peanuts  

10.9 

-j»  6 

0   O 

•o 

19o 

rn    A 

0/'4 

Composition  of  Ether  Extract. — The  composition  of  the  ether 
extract  of  some  plants  is  contained  in  the  following  table  :l 
PERCENTAGE  COMPOSITION  OF  ETHER  EXTRACT. 


Neutral  fat 

Free 
fatty  acid 

lecithin 

Unsaponi- 
fiable  matter 

Hay      

23-7 
78.3 
59-2 
53.6 

95-5 
24.7 
92.9 

16.3 
23.0 

37-3 
16.4 

35-4 

II.  2 

1.2 
3O.I 

56.9 

35-3 

trace 

3-3 
0.8 
27.4 

It 

4-4 

3-i 

30.8 

7-6 

2.7 
7-4 
1.5 
34-5 
i.i 
10.9 
10.7 

Qats  

peas  

Potatoes                      .... 

Beets                        

Stellwaag  found,  according  to  the  above  table,  that  nearly  one- 
third  of  the  ether  extract  of  hay  and  malt  sprouts  is  unsaponifiable 
matter.  The  ether  extract  of  rye  bran,  peas,  potatoes,  and  beets 
contain  about  10  per  cent,  unsaponifiable  matter.  Over  one- 
fourth  of  the  ether  extract  of  peas  consists  of  lecithin. 

According  to  Fraps  and  Rather,2  who  examined  18  hays  and 
fodders,  from  39  to  71  per  cent,  of  the  ether  extract  consists  of 
non-fats,  chiefly  wax  alcohols.  The  average  percentage  of  non- 
fats  was  58  per  cent,  of  the  ether  extract. 

1  Stellwaag,  Landw.  Versuchs-stat. 

2  Bulletin  150,  Texas  Station. 


350 


PRINCIPLES  OF  AGRICULTURAL   CHEMISTRY 


PERCENTAGE  COMPOSITION  OF  ETHER  EXTRACT 


Unsaponi- 
fiable  matter 

Saponifiable 
matter 

Alfalfa  ha}*  •    •  •  *              

67 

6c 

JO 

27 

?b 
60 

7Q 

oy 

71 
60 

3 

71 

o° 
26 

Millet  hay          

16 
1Q 

ro 

6y 
«;8 

D^ 
16 

ow 

Determination  of  Ether  Extract. — The  substance  is  dried  and 
extracted  with  water-free  ether  for  sixteen  hours.     The  ether  is 


C— 


A— 


Fig.  79. — Fat  extraction  apparatus. 

then  distilled  off,  and  the  fat,  after  having  been  dried  in  a  water 
oven,  is  weighed.     A  form  of  apparatus  is  represented  in  the 


CONSTITUENTS   OF    PLANTS  351 

figure.  The  ether  vaporized  from  the  flask  A  is  condensed  by 
the  cool  water  running  through  the  condenser  B  and  drops  on  the 
substance  in  C.  It  dissolves  the  ether  extract  and  returns  to  the 
flask  A,  carrying  the  fat  with  it.  It  is  then  ready  to  be  vaporized 
again  and  extract  a  fresh  quantity  of  fat.  When  the  exhaustion  is 
complete,  the  ether  is  evaporated  off  and  the  fat  is  dried  and 
weighed.  This  method  is  liable  to  several  sources  of  errors,  as 
follows : 

(1)  Loss  of  volatile  fatty  acids  during  the  drying  of  the  sub- 
stance or  of  the  extract. 

(2)  Oxidation  of  fats  if  the  preliminary  drying  of  the  material 
is  carried  out  in  the  air. 

Fats  and  Oils.1 — The  largest  and  the  most  important  portion  of 
the  ether  extract  of  concentrated  feeds  is  composed  of  fats  and 
oils.  Fats  are  solid  at  the  ordinary  temperature,  while  oils  are 
liquid.  They  consist  of  ethereal  salts,  termed  glycerides,  which 
are  compounds  of  certain  fatty  acids  with  the  tribasic  alcohol, 
glycerol,  C3H-,(OH)3;  thus,  the  fat  palmitin  C3H5(C15H31COo)3, 
is  the  glyceride  of  palmitic  acid  C15H31CO2H.  When  heated  with 
alkalies,  fats  form  glycerol  and  salts  of  the  fatty  acids,  which  are 
soaps.  The  process  is  called  saponification.  For  example : 
QH5(C]5H31C02)3  +  3NaOH  =  C3H5(OH)3  +  3C15H31CO2Na. 
Palmitin  -|-  Sodium  hydroxide  =  Glycerol  +  Sodium  palmitate. 

All  fats  are  lighter  than  water  and  insoluble  in  it.  When  pure, 
they  are  colorless,  odorless,  and  neutral  in  reaction;  under  con- 
tinued exposure  to  air,  they  begin  to  turn  yellow,  acquire  a  dis- 
agreeable odor  and  taste,  and  become  acid — that  is,  the  fat  be- 
comes rancid.  The  rancidity  is  due  to  partial  decomposition  of 
the  glycerides,  fatty  acids  being  formed  which  are  partly  oxidized 
by  the  air  to  volatile  substances  having  a  disagreeable  odor. 

Oils  are  divided  into  the  non-drying  oils,  and  the  drying  oils. 
The  drying  oils,  of  which  linseed  oil  may  serve  as  an  example, 
are  oxidized  by  the  air  to  solid,  varnish-like  masses.  They  con- 
tain linolin  and  linolenin,  which  are  the  glycerides  of  unsaturated 
acids.  The  non-drying  oils  do  not  undergo  this  change. 
1  See  Lewkowitsch,  Oils,  Fats  and  Waxes. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Fats  and  oils  are  concentrated  forms  of  nutrition,  containing 
more  nourishment  and  energy  than  any  other  nutrient  in  feeding 
stuffs  (2  J4  times  as  much  as  carbohydrates). 

The  following  table  shows  the  formula  and  composition  of  the 
principal  glycerides  which  occur  in  fats. 

COMPOSITION  OF  FATS. 


Name 

Glyceride   of 

Formula 

Butyric  acid 
Caproic  acid 
Laurie  acid 
Caprylic  acid 
Palmitic  acid 
Stearic  acid 
Oleic  acid 
Linolinic  acid 
Linolinic  acid 

C3H5(C3H7C02)3 
C3H5(C5HnC02)3 
C3H5(CnH23C02)3 
C3H5(C7H15C02)3 
C3H5(C15H31C02)3 
C3H5(C17H35C02)3 
C3H5(C17H33C02)3 
CSH5(C17H81C02)8 
C3H5(C18H29C02)3 

Caprylin  

Palmitin  

Stearin  

Olein  

Palmitin,  stearin,  olein,  linolin,  and  laurin  are  the  principal 
glycerides  which  occur  in  fats  and  oils.  Laurin,  palmitin,  and 
stearin  are  solid  at  the  ordinary  temperature,  while  olein  is 
liquid.  The  consistency  of  a  fat  depends  upon  the  predominating 
glycerides;  the  fats  rich  in  palmitin  and  stearin  are  solid,  while 
those  rich  in  olein  or  linolin  are  liquid.  Animal  fats  and  oils  con- 
tain the  same  glycerides  as  vegetable  fats  and  oils. 

The  glycerides  which  occur  in  some  fats  and  oils  are  named 
below : 

Corn  oil,  chiefly  olein  and  linolin,  some  stearin. 

Cottonseed  oil,  chiefly  linolin,  also  stearin,  palmitin,  and  olein. 

Sunflower  oil,  chiefly  linolin. 

Linseed  oil,  linolin,  linolenin,  isolenin,  olein,  stearin,  palmitin. 

Peanut  oil,  stearin,  olein,  linolin,  arachiden. 

Olive  oil,  chiefly  olein,  some  palmitin  and  stearin. 

Cocoanut  oil,  myrestin,  laurin,  palmitin,  olein,  caproin,  caprylin. 

Examination  of  Fats  and  Oils. — Different  proportions  of  the 
same  glycerides  often  occur  in  fats  and  oils  of  different  origin. 
The  following  general  methods  are  applied  in  the  testing  of  fats 


CONSTITUENTS  OF  PLANTS  353 

and  oils.  Specific  tests  may  be  made  to  detect  certain  oils,  such 
as  cottonseed  oil. 

The  specific  gravity  is  of  importance. 

The  index  of  refraction  is  the  measure  of  the  extent  to  which 
the  fat  bends  a  ray  of  light  passing  through  it.  It  affords  a 
rapid  method  for  testing  the  purity  of  some  oils. 

The  saponification  value  is  estimated  by  saponifying  a  weighed 
quantity  of  fat  with  a  solution  containing  a  known  amount  of 
alkali,  and  estimating  the  unused  alkali  by  titration  with  an  in- 
dicator and  an  acid  of  known  strength.  It  is  usually  expressed 
in  terms  of  milligrams  of  alkali  neutralized  by  one  gram  fat. 

The  volatile  acids  are  estimated  by  saponifying  a  weighed  quan- 
tity of  fat,  liberating  the  fatty  acids  with  a  non-volatile  acid,  and 
distilling  off  the  volatile  acids  with  water.  The  distillate  is 
titrated  with  alkali  of  known  strength.  This  method  is  especially 
valuable  for  butter,  since  it  is  the  only  ordinary  fat  which  contains 
glycerides  of  volatile  fatty  acids. 

The  iodine  value  is  estimated  by  treating  a  weighed  amount  of 
fat  with  a  solution  containing  a  known  amount  of  iodine.  After 
sufficient  time,  the  uncombined  iodine  is  titrated  and  so  estimated. 
The  iodine  combines  with  the  unsaturated  fats,  and  not  with  the 
saturated,  so  that  the  quantity  of  iodine  absorbed  depends  on  the 
quantity,  and  the  condition  of  unsaturation  of  the  fats  present. 
The  iodine  number  is  the  milligrams  of  iodine  which  combine  with 
one  gram  of  oil.  The  iodine  number  is  a  valuable  index  to  the 
nature  and  purity  of  many  oils. 

Free  fatty  acids  are  often  present  in  the  ether  extract.  If  the 
substance  is  old,  and  the  fat  in  it  has  become  rancid,  a  large  part 
of  the  ether  extract  may  consist  of  free  fatty  acids.  They  come 
from  the  hydrolysis  or  decomposition  of  the  fats  into  fatty  acids 
and  glycerol.  If  acids  of  low  boiling  point  are  present,  the  free 
acids  are  partly  volatilized  when  the  substance  is  dried  before 
being  extracted  with  ether,  or  when  the  ether  extract  is  dried. 
They  are  best  determined  by  extracting  the  substance  without 
drying,  and  titrating  the  etheral  solution  with  a  standard  solution 
of  caustic  potash,  with  the  addition  of  alcohol. 


354  PRINCIPLES   OF    AGRICULTURAL    CHEMISTRY 

Lecithins. — These  are  wax-like  bodies  which  resemble  fats  in 
some  respects.  They  contain  nitrogen  and  phosphorus.  Like 
fats,  they  are  saponified  by  alkalies.  When  saponified  they  yield 
a  soap,  cholin,  phosphoric  acid,  and  glycerol.  The  quantity  of 
lecithin  in  the  ether  extract  is  calculated  from  the  amount  of 
phosphoric  acid  found  in  it.  The  magnesium  pyrophosphate 
multiplied  by  7.25  is  assumed  to  represent  the  lecithin.  Calcium 
and  magnesium  phosphates  have,  however,  been  found  in  the  ether 
extract  of  plants,  their  presence  being  attributed  to  the  presence  of 
metallic  glycero-phosphates  soluble  in  ether.  When  these  sub- 
stances are  present,  the  amount  of  lecithin  in  the  fat  is  less  than 
the  amount  calculated  from  the  phosphoric  acid  present. 

Lecithin  is  not  entirely  extracted  by  ether  from  plant  substance, 
but  is  completely  extracted  when  the  ether  extraction  is  followed 
by  extraction  with  absolute  alcohol.  If  the  alcoholic  solution  is 
evaporated  at  40-50°  C.  and  the  residue  taken  up  with  ether  and 
purified  by  shaking  with  water,  the  lecithin  can  be  obtained  fairly 
pure. 

Leguminous  seeds  are  relatively  rich  in  lecithin;  the  cereals 
(wheat,  rye,  and  corn)  contain  much  less.  The  table  below  shows 
the  lecithin  content  of  some  substances: 

LECITHIN  IN  PLANTS. 

Per  cent, 
in  dry  matter 

Young  grass 0.45 

Young  vetch  plants 0.86 

Yellow  lupine  seeds 1.55 

Soja  bean i  .64 

Peas 1.23 

Wheat   0.65 

Rye 0.57 

Corn 0.74 

Sunflowers 0.44 

Vetch 0.98 

The  alcoholic  extract  contains  not  only  lecithin,  but  other 
organic  compounds  containing  phosphorus,  some  of  which  con- 
tain sugar.  Lecithin  is  of  considerable  value  to  the  animal  and 


CONSTITUENTS  OF  PLANTS  355 

also  to  the  plant.  It  aids  in  the  assimilation  and  transportation  of 
the  fat. 

Hydrocarbons  are  compounds  of  hydrogen  and  carbon.  They 
have  been  detected  in  the  unsaponifiable  portion  of  the  ether 
extract  of  plants.  The  ether  extract  of  meadow  hay  contains  a 
hydrocarbon,  probably  C27HI56.  Tobacco  contains  I  per  cent,  of 
the  hydrocarbons  C31H64  and  C27H56. 

Wax  Alcohols. — The  unsaponifiable  matter  consists  of  phytos- 
terol  and  other  alcohols.  Phytosterol  C28H34(OH)  is  a  solid 
alcohol  which  crystallizes  from  alcohol  in  glistening  plates.  It 
gives  characteristic  color  reactions  with  certain  reagents. 

The  separation  of  phytosterol  and  Hydrocarbons  from  the  fats 
is  based  upon  the  fact  that  while  alkalies  act  upon  fats  to  form 
compounds  soluble  in  water  (soaps),  the  phytosterol  or  hydro- 
carbons are  not  affected.  The  ether  extract  is  saponified,  and 
the  soap  extracted  with  ether,  which  dissolves  the  phytosterol  and 
hydrocarbons.  The  etheral  solution  is  evaporated,  and  the 
phytosterol  purified  by  crystallization  from  alcohol. 

Wax  alcohols  are  found  in  considerable  proportions  in  the 
ether  extract  of  hays  and  straws.  They  are  digested  to  a  certain 
extent  by  animals,  though  not  so  well  as  fats.  The  alcohols  pres- 
ent are  probably  myricyl  alcohol  C30H61OH,  and  other  similar 
alcohols  of  lower  molecular  weight. 

Chlorophyll. — This  is  the  green  coloring  matter  of  leaves.  It 
contains  nitrogen.  It  is  soluble  in  ether,  and  gives  a  green  color 
to  the  ether  extract  from  hays  and  green  plants.  Its  exact  com- 
position is  unknown.  When  the  ether  extract  containing 
chlorophyll  is  saponified,  and  the  unsaponified  material  is  ex- 
tracted by  means  of  ether,  the  chlorophyll  remains  with  the  fatty 
acids  and  colors  them  green. 

Protein. — Protein  is  the  nitrogen  of  the  plant  multiplied  by 
6.25  and  includes  all  the  nitrogenous  compounds  of  feeding  stuffs. 
Protein  includes  amides,  alkaloids,  and  inorganic  nitrogen  com- 
pounds (if  present).  Protein  is  found  in  all  parts  of  all  plants, 
as  it  is  necessary  to  the  life  and  growth  of  the  plant.  It  is  trans- 
ferred from  the  stem  and  leaves  of  plants  to  the  seed  when  the 


356  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

plant  matures.  Protein  is  especially  abundant  in  leguminous 
plants,  and  in  seeds,  particularly  the  seeds  of  legumes.  The  fol- 
lowing table  shows  the  amounts  of  protein  in  some  vegetable  sub- 
stances : 

PROTEIN  IN  VEGETABLE  MATERIALS. 

Per  cent. 

Corn  fodder,  green 1.8 

Potatoes 2.1 

Onions 1.4 

Timothy,  green 3.1 

Red  clover,  green 4.4 

Corn,  grain 10.5 

Wheat,  grain 11.9 

Cowpeas,  grain  20.8 

Corn  fodder 4.5 

Timothy  hay 5.9 

Red  clover  hay 12.3 

Cowpea  hay 16  6 

Soja  beans 34.0 

The  nitrogenous  constituents  of  agricultural  plants  may  be 
divided  into  the  four  following  groups:  (i)  proteids;  (2)  amides 
and  amido  acids;  (3)  inorganic  compounds;  (4)  miscellaneous 
bodies ;  which  include  alkaloids,  lecithin,  chlorophyll,  etc.  Pro- 
teids and  amides  are  of  common  occurrence  in  agricultural  prod- 
ucts ;  the  other  bodies,  while  of  some  importance,  are  of  less 
general  occurrence. 

Proteids. — Proteids  are  complex  bodies  of  unknown  high  mole- 
cular weight  and  unknown  .constitution.  They  contain  carbon, 
hydrogen,  oxygen,  nitrogen,  sulphur,  and  sometimes  phos- 
phorus. Proteids  are  exceedingly  important,  being  necessary 
to  the  life  of  both  plants  and  animals.  The  flesh  of  animals  is 
composed  largely  of  proteids,  which  are  derived  from  vegetable 
proteids.  When  split  up,  proteids  yield  various  amides,  amido 
compounds,  and  other  bodies.  This  splitting  up  takes  place  dur- 
ing digestion,  and  the  digested  constituents  are  reunited  in  the 
animal  body  to  form  animal  proteids,  which  are  different  from 
the  original  vegetable  proteids.  The  splitting  up  also  takes  place 
in  the  germination  of  seeds,  when  the  reserve  proteids  are  broken 
up  into  asparagin  and  other  bodies,  and  used  in  the  production 
of  new  tissue  in  the  growing  portions  of  the  plant. 


CONSTITUENTS  OF  PLANTS  357 

Classes  of  Proteids.1— The  proteids  are  divided  into  three 
groups;  simple  proteids,  conjugated  proteids,  and  derived 
proteids. 

I.  SIMPLE  PROTEIDS. — (a)  Albumins. — Albumins  are  soluble 
in  water  and  are  not  precipitated  by  sodium  chloride,  or  mag- 
nesium sulphate.     They  are  coagulated  and  made  insoluble  by 
heat.     The  best  example  of  an  albumin  is  the  white  of  an  egg. 

(b)  Globulins. — Globulins  are  not  soluble  in  water,  but   are 
soluble  in  solutions  of  sodium  chloride,  and  other  neutral  salts. 
They  are  precipitated  by  removing  the  salts,  or  by  saturating  the 
solution  with  salts. 

(c)  Protamins  are  proteids  soluble  in  alcohol.     Several  have 
been  isolated.     Gliadin  is  found  in  wheat ;  zein,  in  Indian  corn, 
etc. 

(d)  Glutelins. — These  are  not  soluble  in  water,  salt  solutions, 
or  alcohol.     The  glutenin  of  wheat  is  the  only  well  characterized 
representative  of  this  group  yet  obtained,  though  there  are  indica- 
tions that  they  may  be  present  in  other  cereals. 

(e)  Albuminiods,  (/)  Histones,  and  (g)  Protamines  have  not 
been  found  in  plants.     They  are  animal  proteids. 

II.  CONJUGATED  PROTEIDS. — Coagulated  proteids  are  complex 
proteids  which  can  be  split  up  into  proteids  and  other  bodies. 
Nueclo-proteids,  formed  from  nucleic  acid  and  protein,  have  been 
isolated  from  some  plants.     Glycoproteids  may  be  split  up  into 
proteids  and  carbohydrates.    Phosphoproteids  contain  phosphorus. 

III.  DERIVED  PROTEIDS. — Derived  proteids  are  produced  from 
proteids  by  the  action   of   acids,   alkalies,  alcohol,  or  digestive 
juices.     The  three  important  groups  are  proteoses,  peptones,  and 
peptides. 

Proteoses. — Proteoses  are  soluble  in  water,  and  are  not 
coagulated  by  heat,  differing  in  this  respect  from  albumins.  They 
are  diff  usable. 

Peptones. — Peptones  are  very  easily  soluble  in  water,  and  are 
not  precipitated  by  heat,  by  neutral  salts,  or  by  nitric  acid.  They 
are  precipitated  by  tannic  acid,  by  absolute  alcohol,  and  by  picric 
1  Osborne,  The  Vegetable  Proteins. 


358 


PRINCIPLES  OF  AGRICULTURAL  CH£MISTPY 


acid.  Proteoses  and  peptones  are  formed  in  the  digestion  of 
proteids  within  the  animal  body,  by  the  action  of  the  juices  of  the 
stomach  (the  gastric  juice),  which  contain  pepsin,  upon  them. 

Proteids  in  Plants. — The  names  and  occurrence  of  some  plant 
proteids  are  as  follows  : 

Legumin,  which  is  found  in  considerable  quantity  in  seeds  of 
pea,  horse  bean,  vetch,  and  lentil. 

Vignin,  the  chief  protein  of  the  cowpea. 

Glycenin,  a  globulin,  chief  protein  compound  of  soy  bean. 

Gliaden,  soluble  in  alcohol  of  70-80  per  cent.,  the  most  abundant 
protein  of  wheat  kernels. 

Hordein,  soluble  in  alcohol,  found  in  barley. 

Zein,  most  abundant  in  corn,  easily  soluble  in  alcohol. 

Vicilin,  a  globulin  found  in  pea,  lentil  and  horse  bean. 

Composition  of  Proteids. — The  proteids  vary  in  composition 
and  properties.  The  percentage  composition  of  some  important 
vegetable  proteids  is  given  in  the  following  table  i1 


c 

H 

N 

S 

o 

51.71 

51.72 
54-29 

5  '-03 
52.72 

52.34 

6.86 

6-95 
6.80 
6.85 
6.86 
6.83 

18.30 
18.04 
17.20 
18.30 
I7.I6 
17-49 

0.62 

°"39 
0.85 
0.69 
I  03 
1.  08 

22.51 

22.90 
20.86 

23-13 
21.73 
22.26 

Globulin   wheat  

The  factor  6.25  used  for  proteids  requires  16.00  per  cent,  nitro- 
gen. The  above  proteids  contain  from  17.20  to  18.30  per  cent, 
nitrogen. 

Amides  and  Amido  Compounds. — Amides,  as  distinguished  from 
proteids,  are  nitrogenous  compounds  of  known  molecular  weights 
and  known  constitution.  They  have  little  value  in  animal  nutri- 
tion. 

In  seeds  they  occur  only  in  small  quantity.  They  are  more 
abundant  in  leaves  and  the  growing  parts  of  plants,  and  are  parti- 
cularly abundant  in  germinating  seeds.  Nitrogenous  material  is 
converted  into  amides  for  the  purpose  of  transportation  through 
1  Osborne,  The  Vegetable  Proteins,  p.  49. 


CONSTITUENTS  OF  PLANTS 


359 


the  plant.  Amides  are  also  formed  from  proteids  by  the  action 
of  acids,  or  the  digestive  juices  of  animals,  or  by  other  agencies. 

The  most  important  amido  compounds  are  leucin,  tyrosin, 
phenyl-amido-proponic  acid,  asparagin,  and  glutamin.  Of  these 
asparagin  is  relatively  the  most  common  and  most  abundant.  It 
has  the  formula  C2H)5(NH2)  (CONH2)  (COOH).  Leucin, 
tyrosin,  and  phenyl-amido-propionic  acid  are  amido-acids ;  that  is 
to  say,  they  are  acids  in  which  the  amido  group  NH2  has 'replaced 
an  atom  of  non-acid  hydrogen.  Thus  leucin,  C5H10(NH2)CO2H, 
is  derived  from  capronic  acid,  C^H^COaH,  by  replacing  an  atom 
of  hydrogen  by  NH2. 

Determination  of  Proteids  and  Amides. — An  accurate  method 
for  this  determination  is  much  to  be  desired.  The  usual  method 
consists  in  boiling  the  substance  with  water  and  precipitating  the 
proteids  with  copper  hydroxide.  The  nitrogen  in  the  precipitate 
multiplied  by  6.25  is  supposed  to  give  the  proteids.  The  differ- 
ence between  the  precipitated  nitrogen  and  the  total  nitrogen,  is 
the  amide  nitrogen. 

PROTEIDS  AND  AMIDES  IN  PLANTS.1     (IN  DRY  MATTER.) 


Proteids 

Amides 

1  1.8 

8.3 
7-9 
9-i 
41.7 
13-9 

10.  1 

16.2 

4.4 
47.2 

5.3 

7.0 
4-7 
3-i 
2.4 
0.6 
3-1 

0.8 

1.2 

0.6 

0.7 

The  preceding  table  shows  that  the  protein  of  seeds  consists' 
mostly  of  proteids,  but  a  considerable  part  of  the  protein  of  hays 
and  fodders  may  consist  of  non-proteid  materials.  The  per- 
centage of  nitrogen  in  the  amido  compounds  we  have  mentioned, 
is  given  in  the  following  table : 

1  Bulletin  172,  North  Carolina  Exp.  Sta. 


360  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

NITROGEN  IN  AMIDO  COMPOUNDS 

Per  cent. 

Asparagin 21.37 

Glutamin 19.31 

Leucin 16.87 

Phenyl-amido-propronic  acid 8.48 

Tyrosin 7-73 

Considering  that  asparagin  is  the  most  common  amide  in  plants, 
it  is  evident  that  the  factor  6.25  (which  requires  16  per  cent, 
nitrogen)  is  too  high.  A  percentage  of  21.37  nitrogen  requires 
the  factor  4.68. 

Inorganic  Nitrogenous  Bodies. — Growing  plants  sometimes  con- 
tain appreciable  amounts  of  nitrates  or  ammonia.  Very  little  is 
found  in  ripe  seeds  or  plants.  The  nitrates  or  ammonia  are 
taken  up  by  the  roots  of  the  plants,  and  used  for  the  production  of 
organic  nitrogenous  bodies. 

Miscellaneous  Nitrogenous  Substances. — Other  nitrogenous  sub- 
stances found  in  plants  are  alkaloids,  lecithin,  chlorophyll,  etc. 

Alkaloids  are  substances  of  poisonous  or  medicinal  character. 
Since  they  are  bases,  they  unite  with  acids  to  form  salts. 
Alkaloids  are  not  found  to  any  extent  in  ordinary  agricultural 
products. 

Lupine  seeds  contain  from  0.02  to  0.65  per  cent,  alkaloids, 
according  to  the  variety.  The  principal  alkaloid  is  called  lupinin. 
The  seeds  are  so  bitter  that,  without  special  preparation,  they  are 
not  eaten  by  animals. 

Tobacco  contains  0.61  to  6.44  per  cent,  alkaloids,  the  chief  be- 
ing nicotine.  In  the  pure  condition  it  is  very  poisonous. 

Caffeine  is  an  alkaloid  found  in  coffee  and  tea,  to  which  they 
owe  a  portion  of  their  properties. 

Chlorophyll  contains  nitrogen,  and  so  is  included  in  protein. 

Nitrogen-Free  Extract.1 — This  term  is  used  for  the  reason  that 
the  material  is  soluble  in  acids  and  alcohols,  and  is  free  from 
nitrogen.  The  nitrogen-free  extract  of  seeds,  and  of  many  con- 
centrated feeds  consists  largely  of  sugars,  starches,  and  similar 
substances,  which  are  easily  digested  and  of  high  value  to  animals. 
But  the  nitrogen-free  extract  of  hays,  straws,  and  fodders  con- 
1  See  Tollens,  Exp.  Sta.  Record  8,  p.  641. 


CONSTITUENTS  OF  PLANTS  361 

tains  only  relatively  small  quantities1  of  sugars  and  starches,  and 
large  amounts  of  less  easily  digested  material. 

The  nitrogen-free  extract  makes  up  the  largest  part  of  most 
agricultural  plants.  In  many  instances  it  is  as  much  as  the  sum 
of  all  the  other  constituents.  The  percentages  in  the  dry  matter 
of  certain  plants  are  given  in  the  following  table : 

NITROGEN-FREE  EXTRACT.     (!N  DRY  MATTER.) 

Per  cent. 

Corn  fodder 60.6 

Timothy  hay 52.8 

Red  clover 45.8 

Cowpea  vines 43.6 

Potatoes 82. 2 

Corn 77.4 

Wheat 80.4 

Co wpeas 65. 5 

Soja  bean 32.2 

The  nitrogen- free  extract  may  contain  sugars,  starches,  pen- 
tosans,  hemi-celluloses,  gums,  vegetable  acids,  and  miscellaneous 
bodies.  It  is  composed  to  a  large  extent  of  carbohydrates. 

Carbohydrates  are  compounds  containing  carbon,  united  with 
hydrogen  and  oxygen  in  the  proportion  to  form  water. 
Chemically,  they  are  related  to  alcohols  and  aldehydes  or  ketones. 
The  general  formula  of  carbohydrates  is  Cm(H2O)n.  Glucose, 
CgH^Oe,  starch  C6H10O5,  and  cane  sugar  (sucrose)  C^H^On, 
are  examples.  Some  carbohydrates  are  soluble  in  water 
and  have  a  sweet  taste,  others  are  insoluble  and  taste- 
less. Some  are  easily  acted  upon  by  chemical  reagents, 
while  others,  (particularly  cellulose)  are  very  resistant.  All 
carbohydrates,  however,  may,  by  appropriate  means,  be  converted 
into  simple  sugars. 

It  is  not  correct  to  use  the  term  "carbohydrates"  to  signify  the 
nitrogen-free  extract.  The  nitrogen-free  extract  consists  partly 
of  substances  other  than  carbohydrates.  Crude  fiber  also  con- 
tains cellulose,  which  is  a  carbohydrate. 

Sugars. — The  sugars  are  carbohydrates  which  are  soluble  in 
water,  and,  as  a  general  rule,  have  a  sweet  taste.     Cane  sugar, 
1  Frear,  Report  Pennsylvania  Station,  1903-4. 
24 


362 


PRINCIPLES  OF  AGRICULTURAL,  CHEMISTRY 


which  is  prepared  from  sugar  cane  or  sugar  beets,  is  the  most 
common  sugar.  Sugars  are  divided  into  two  groups :  the  simple 
sugars,  or  monosaccharides,  represented  by  glucose,  and  the  com- 
plex sugars,  or  polysaccharides,  represented  by  cane  sugar  or  suc- 
rose. The  complex  sugars  can  be  split  up  into  one  or  more  kinds 
of  simple  sugars.  The  sugars  can  all  be  crystallized,  but  in  some 
cases  crystallization  is  difficult. 


Fig.  80. — A  polariscope. 

Sugars  are  acted  upon  by  acids  and  alkalies,  forming  various 
products,  some  of  which  are  brown  in  color.  Boiled  with  con- 
centrated hydrochloric  acid,  cane  sugar  gives  a  black  precipitate 
called  humic  acid,  the  name  being  given  chiefly  on  account  of  its 
black  color. 

Optical  Properties  of  Sugars. — If  a  ray  of  light  is  passed 
through  a  crystal  of  Iceland  spar,  it  is  split  up  into  two  rays, 
having  peculiar  properties,  and  called  polarized  light.  If  a  ray 
of  this  polarized  light  falls  upon  another  parallel  crystal,  in  one 
position  no  light  will  pass  through ;  if  the  crystal  is  rotated  at  an 
angle  of  45°,  all  the  light  goes  through,  while  in  intermediate  posi- 
tions only  a  part  is  transmitted. 

If  the  two  crystals  referred  to  above  are  placed  so  that  all  the 
light  passes  through,  and  a  solution  of  sugar  then  placed  between 
them,  the  polarized  light  will  no  longer  all  go  through  the  second 
prism,  but  the  prism  must  be  rotated  to  a  certain  angle  before  the 
light  will  all  pass  through.  The  sugar  has  twisted  the  ray  of 


CONSTITUENTS  OF  PLANTS  363 

polarized  light,  or  as  it  is  termed,  it  has  rotated  the  plane  of 
polarization.  The  degree  of  rotation  depends  on  the  kind  of 
sugar,  the  strength  of  the  solution,  the  length  of  the  column,  and 
the  temperature. 

A  polariscope1  consists  essentially  of  two  Nicol  prisms  of  Ice- 
land spar  properly  mounted,  between  which  the  substance  is 
placed,  having  lenses  for  suitable  management  of  the  light  and 
the  image.  In  order  to  measure  the  rotation,  either  the  second 
crystal  (called  the  analyzer)  may  be  rotated,  and  the  angle  of 
rotation  read,  or  the  rotation  may  be  compensated  by  a  quartz 
wedge,  which  is  likewise  read  on  a  graduated  scale.  Several 
arrangements  are  made  in  order  that  the  reading  may  be  accurate. 
In  one  type  of  instrument,  the  circular  ray  of  polarized  light  is 
split  into  two  half-discs,  so  that  if  the  crystal  or  quartz  wedge  is 
moved  slightly  to  the  right,  one-half  of  the  image  becomes  dark, 
and  if  it  is  moved  slightly  to  the  left,  the  other  half  becomes 
dark.  The  intermediate  position,  at  which  both  sides  are  of 
equal  brightness,  is  the  one  at  which  the  reading  is  taken.  The 
instrument  can  be  adjusted  so  that  only  a  very  slight  change 
throws  the  shadow  on  the  one  side  or  the  other. 

The  polariscope  affords  a  very  rapid  and  accurate  method  for 
estimating  sugar,  especially  cane  sugar,  and  it  is  used  extensively 
in  the  analysis  of  sugar,  sugar  cane,  sugar  beets,  and  in  the  con- 
trol of  the  processes  of  manufacture  of  sugar  from  cane  or  beets. 

Reducing  Power. — When  simple  sugars  and  certain  compound 
sugars  are  boiled  with  copper  salts  in  alkaline  solution,  the  copper 
is  reduced  to  cuprous  oxide  (Cu,2O),  and  may  be  collected  and 
weighed  as  such,  or  as  metallic  copper.  This  property  is  used 
for  the  detection  of  sugars,  and  also  for  their  quantitative  estima- 
tion. The  amount  of  sugar  solution  required  to  reduce  a  given 
amount  of  copper  may  be  used  to  measure  the  amount  of  sugar. 
The  amount  of  copper  reduced  depends  upon  the  nature  of  the 
sugar,  the  volume  of  the  solution,  the  time  of  heating,  the  com- 
position of  the  copper  solution,  and  other  details  of  the  analytical 
process. 

1  See  Wileys  Principles  and  Practice  of  Agr.  Chem  Anal.,  Vol.  III. 


364  PRINCIPLES  OF  AGRICUI/TURAI,  CHEMISTRY 

Tables  have  been  prepared  showing  the  amounts  of  copper 
which  were  found  by  experiments  to  be  reduced  by  given  sugars 
under  fixed  conditions ;  these  tables  can  be  used  in  the  estimation 
of  sugars  under  the  same  conditions,  but  the  details  of  the  method 
used  in  preparing  the  tables  must  be  followed  carefully. 

The  copper  solutions  used  ordinarily  are  Fehling's   solution, 
containing  fixed  quantities  of  copper  sulphate,  sodium  potassium 
tartrate,  and  sodium  hydroxide;  and  Allihn's  solution,  containing 
certain  amounts  of  copper  sulphate,  sodium  potassium  tartrate 
and  potassium  hydroxide.     Other  solutions  are  used.     Different 
sugars  require  different  quantities  of  copper  under  the  same  con- 
ditions.    For  example,  the  same  amount  of  copper  will  be  reduced 
from  Sachsse's  solution  by  the  following  amounts  of  sugars : 
Fructose  213  mg. 
Maltose  491  mg. 
Lactose  387  mg. 

Fermentation. — Under  suitable  conditions,  yeast  converts  cer- 
tain sugars  into  alcohol  and  carbon  dioxide  according  to  the 
following  reaction : 

C6H1206  =  2C2H60  +  2C02. 

Yeast  is  a  plant  which  grows  in  the  solution,  and  develops  an 
enzyme  which  changes  the  sugar  as  described.  Like  all  plants, 
yeast  must  have  nitrogenous  food,  also  phosphoric  acid,  potash, 
and  lime.  Yeast  will  not  grow  well  in  pure  sugar.  An  enzyme 
is  a  substance  which  causes  a  chemical  change,  without  itself  be- 
ing changed  in  the  reaction. 

The  simple  hexoses  are  easily  fermented.  Some  of  the  com- 
pound hexose  sugars  ferment  readily,  while  others  must  first  be 
split  up  into  the  simple  hexoses.  Pentosans  do  not  undergo  the 
alcoholic  fermentation. 

There  are  other  kinds  of  fermentation,  probably  the  most  im- 
portant being  the  acetic  fermentation,  in  which  alcohol  is  con- 
verted into  acetic  acid  (vinegar),  and  the  lactic  acid  fermentation, 
in  which  sugar  is  converted  into  lactic  acid.  This  takes  place  in 
the  souring  of  milk. 


CONSTITUENTS  OF  PLANTS  365 

Fermentation  is  important  in  the  manufacture  of  cider  from 
apple  juice;  wine  from  grape  juices;  and  alcoholic  beverages  and 
alcohol  from  materials  containing  starch  or  sugar,  such  as 
potatoes,  corn,  rye,  barley,  etc. 

Classes  of  Simple  Sugars. — Four  groups  of  simple  sugars  are 
known  to  chemists,  though  only  two  of  these  are  of  agricultural 
importance.  The  groups  are :  ( i )  the  trioses,  containing  three  car- 
bon atoms  in  the  molecule  C3H6O3;  (2)  the  tetroses,  containing 
four  carbon  atoms,  C4H8O4;  (3)  the  pentoses,  containing  five 
carbon  atoms;  and  (4)  the  hexoses,  containing  six.  All  the 
natural  carbohydrates  are  related  to  either  the  pentoses  or  the 
hexoses.  The  principal  simple  sugars  are  xylose  and  arabinose, 
which  are  pentoses ;  and  glucose,  fructose,  mannose,  and  galactose, 
which  are  hexose  sugars. 

Each  of  these  sugars  exists  in  three  modifications,  namely,  one 
which  rotates  polarized  light  to  the  right,  one  which  rotates 
polarized  light  to  the  left,  and  one  which  does  not  rotate  it,  and 
is  inactive.  Thus  we  have  d-glucose,  1-glucose  and  i-glucose, 
dextro-,  laevo-,  and  inactive  glucose.  Although  many  of  these 
sugars  are  known,  as  a  rule  only  one  modification  of  each  sugar 
is  of  natural  occurrence.  Thus  natural  glucose  is  dextro-rotatory, 
and  was  formerly  called  dextrose  for  this  reason,  and  ordinary 
fructose  is  laevo-rotatory,  and  was  called  levulose. 

Pentose  Sugars,  C5H10O5. — The  pentose  sugars  occur  to  a  very 
limited  extent,  if  at  all,  in  nature.  They  are  of  agricultural  im- 
portance on  account  of  their  relation  to  the  pentosans,  which  are 
found  in  large  quantities  in  agricultural  products. 

When  distilled  with  strong  hydrochloric  acid,  the  pentoses  and 
pentosans  are  converted  into  furfural,1  which  distils  over  with  the 
acid: 

C3H1008  =  C5H402  +  3H20 
Pentose        Furfural 

The  furfural  can  be  precipitated  with  a  solution  of  phloro- 
glucinol,  the  product  being  furfural  phloroglucid.  The  precipitate 
is  filtered  off,  dried,  and  weighed.      The  quantity  of   furfural 
1  Landw.  Versuchs-stat. ,  42,  p.  381. 


366  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

yielded  by  the  different  pentose  sugars  and  pentosans  under  the 
conditions  of  the  work  have  been  determined  by  experiments. 

Stoklosa  found  considerable  quantities  of  water-soluble  pen- 
tosans in  sugar  beet  seed,  and  DeChalmot  found  small  quantities 
in  the  leaves  and  bark  of  a  number  of  plants.  But  pentose  sugars 
have  not  been  separated  as  such  from  plants,  but  are  prepared  by 
the  hydrolysis  of  certain  pentosans.  The  pentoses  do  not  fer- 
ment with  yeast. 

Arabinose,  C5H10O5  =  CH2OH(CHO)3CHO,  has  been  pre- 
pared from  the  pentosans  found  in  lupines,  soja  beans,  rye  bran, 
wheat  bran,  plums,  and  cherry  gum.  It  is  easily  prepared  by  boil- 
ing cherry  gum  with  2  per  cent,  sulphuric  acid.  It  crystallizes 
beautifully,  and  has  a  sweet  taste,  but  not  as  sweet  as  sucrose. 

Xylose,  C5H10OI5,  has  been  prepared  from  beech  wood,  jute,  fir 
wood,  cherry  wood,  laurel  wood,  wheat  straw,  corn  cobs,  oat 
straw,  rye  straw,  corn  bran,  apples,  etc.  It  crystallizes  in  prisms. 

Rhamnose,  C6H,BO3  =  CH3(CHOH)4CHO,  is  methyl  pen- 
tose, which  yields  methyl  furfural  by  distillation  with  hydro- 
chloric acid.  It  is  obtained  from  certain  glucosides,  and 
crystallizes  in  beautiful,  sweet  crystals. 

Hexose  Sugars,  C6H12O6. — The  two  hexose  sugars  of  common 
occurrence  are  fructose  and  glucose.  They  occur,  in  equal 
quantity,  in  sweet  fruits,  flowers,  certain  vegetables.  The  other 
hexoses  are  formed  by  the  hydrolysis  of  certain  carbohydrates. 
All  the  hexoses  are  fermented  by  yeast. 

d-Glucose,  C6H10O5,  or  grape  sugar,  occurs  in  grapes,  sweet 
fruits,  tomatoes,  seeds,  roots,  leaves,  flowers,  honey,  etc.  To- 
gether with  fructose,  it  is  formed  by  the  hydrolysis  of  cane  sugar. 
It  is  also  formed  by  the  hydrolysis  of  starch,  and  is  the  chief 
ingredient  of  many  syrups.  Nitric  acid  oxidizes  it  to  saccharic 
acid,  and  glucose  may  be  detected  by  means  of  this  reaction.  It 
is  also  detected  through  its  optical  properties.  Glucose  is  a  white 
crystalline  substance,  which  is  not  so  sweet  as  cane  sugar.  It  is 
easily  soluble  in  water  and  alcohol.  It  undergoes  fermentation  of 
various  kinds  readily.  Glucose  is  produced  commercially  by  the 


CONSTITUENTS   OF   PLANTS 


367 


action  of  dilute  acids  upon  starch.  The  acid  splits  up  the 
starch,  and  causes  it  to  unite  with  water 

(C6H1005)  +  X  H20  =  C6H1206- 
Starch.  Glucose. 

The  thick  syrup  formed  after  the  acid  is  neutralized  and  the  solu- 
tion evaporated  is  called  glucose  syrup  or  corn  syrup.  It  does 
not  consist  of  pure  glucose.  If  a  solid  mass  is  produced,  it  is 
called  grape  sugar. 

Fructose,  C6H10O5,  accompanies  glucose  in  most  fruits  and 
vegetables.  It  is  difficult  to  crystallize.  It  is  obtained  by  hydrolysis 
of  inulin.  So-called  invert  sugar  is  a  mixture  of  equal  quantities 
glucose  and  fructose,  and  is  formed  by  the  hydrolysis  of  sucrose. 
Honey  is  a  natural  invert  sugar,  dissolved  in  water,  with  small 
quantities  of  impurities.  While  glucose  may  be  separated  from 
invert  sugar  comparatively  easily,  it  is  not  easy  to  separate 
fructose  on  account  of  its  difficult  crystallizability. 

Mannose,  C6H10OD,  has  not  been  found  in  nature.  It  has  been 
prepared  by  the  hydrolysis  of  vegetable  ivory,  the  seeds  of  palms 
and  lilies,  coffee  beans,  and  gum  arabic,  etc. 

Galactose,  C6H10O5,  has  not  been  found  as  such  in  nature.  It 
is  a  product  of  the  hydrolysis  of  milk  sugar,  and  of  carbohydrates 
found  in  seeds  of  lupines,  beans,  soja  beans,  peas,  vetch,  cress, 
young  clover,  lupine,  and  lucerne  plants,  in  gum  arabic,  fruits  of 
pears,  etc.  Nitric  acid  oxidizes  it  to  mucic  acid,  which  is  almost 
insoluble  in  water.  A  method  for  its  estimation  is  based  upon 
this  fact. 

Compound  Sugars. — The  most  important  compound  sugars  are 
cane  sugar,  milk  sugar,  raffinose,  maltose,  and  stachyose.  They 
are  derived  exclusively  from  hexoses. 


Name  and  Formula 

Hydrolized  to 

Action  towards 
Fehling  solution 

Glucose  and  fructose 

No  action 

\^anc  sugar,  Ma^n^i] 

TVTillr    one/sir     O     "FT     O 

Glucose    sralactose 

Reduces 

Glucose 

Reduces 

T?  oflfJtinQf*     OHO 

Glucose  fructose  galactose 

No  action 

Glucose  fructose  glucose 

No  action 

368  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Like  the  monosacchosides,  the  polysaccharides  are  neutral, 
sweet,  colorless  compounds,  easily  soluble  in  water,  and  they  are 
readily  crystallizable.  They  are  easily  converted  into  mono- 
saccharides  by  the  action  of  warm  dilute  acids,  or  certain  un- 
organized ferments.  The  ease  with  which  this  action  takes  place 
depends  upon  the  nature  of  the  sugar;  simply  warming  for  a 
short  time  with  a  dilute  acid  is  sufficient  to  split  cane  sugar 
(sucrose)  into  glucose  and  fructose,  while  maltose  requires  to  be 
boiled  for  some  hours  with  the  acid  for  complete  inversion. 

Sucrose,  CnH^On,  is  prepared  from  sugar  cane,  sugar  beets, 
and  maple  sap.  The  impurities  which  accompany  the  sugar 
are  different  when  prepared  from  these  three  sources,  but  no 
differences  can  be  detected  in  the  sugar  when  it  has  been  thor- 
oughly purified. 

Sucrose  is  widely  distributed.  The  juice  of  sugar  cane,  sweet 
sorghums,  and  sugar  beets  contains  10  to  20  per  cent. 
Peanuts  contain  4-6  per  cent.,  sweet  potatoes  1-3  per  cent.,  the 
seeds  of  beans,  peas,  vetch,  soja  beans,  hemp,  and  sunflower  seeds 
contain  4-6  per  cent.  Some  fruits  contain  5  per  cent,  or  more. 
Green  corn,  before  the  ears  are  formed,  is  quite  rich  in  sucrose. 

Sucrose  crystallizes  in  regular  crystals  belonging  to  the 
monocline  system.  It  is  easily  soluble  in  water  and  has  a  high 
dextro-rotatory  power.  It  melts  at  160°  C.  and  solidifies  on  cool- 
ing to  an  amorphorous  glassy  mass.  A  high  temperature  con- 
verts it  into  a  substance  known  as  caramel,  which  is  used  for 
coloring  some  food  materials.  A  still  higher  temperature  car- 
bonizes it  with  evolution  of  gases  and  vapors. 

Sucrose  does  not  reduce  Fehling's  solution,  but  can  easily  be 
converted  into  invert  sugar,  which  has  reducing  power.  This  is 
a  method  for  its  estimation.  The  polariscope  is  also  used  for  the 
estimation  of  sugar.  The  inversion  of  sugar  takes  places  in  the 
ripening  of  some  fruits,  the  curing  of  fodders,  and  in  the  cooking 
and  preparation  of  human  foods. 

Manufacture  of  Sugar. — The  processes  of  manufacture  from 
sugar  cane  and  sugar  beets  vary  somewhat  in  details.  The  beets 
are  first  sliced,  and  the  sugar  extracted  with  warm  water  or  sugar 


CONSTITUENTS  OF  PLANTS  369 

solution,  in  a  series  of  vessels.  The  water  comes  in  contact  first 
with  beet  slices  nearly  exhausted  of  sugar,  then  it  is  brought  in 
contact  with  slices  richer  in  sugar,  and  finally  passes  through  the 
vessel  containing  fresh  beet  slices.  This  system  exhausts  the 
beet,  and  at  the  same  time  secures  a  comparatively  strong  solu- 
tion of  sugar. 

The  sugar  juice  is  acid.  It  is  treated  with  lime  to  neutralize 
the  acid,  which  would  otherwise  invert  the  cane  sugar  when  the 
juice  is  heated  and  decrease  the  yield.  The  lime  also  precipitates 
a  quantity  of  impurities.  The  lime  which  goes  into  solution  is 
next  precipitated  with  carbon  doxide  and  the  solution  is  finally 
neutralized  and  bleached  with  sulphur  dioxide. 

The  sugar  solution  is  next  evaporated  until  the  sugar  is  ready 
to  crystallize.  Since  inversion  would  take  place  at  the  tempera- 
ture required  for  rapid  evaporation  in  the  open  air,  and  since 
there  would  also  be  danger  of  burning,  the  evaporation  is  carried 
on  in  a  vacuum,  in  which  the  solution  boils  at  a  comparatively 
low  temperature.  The  solution  is  drawn  off  when  the  sugar  is 
ready  to  crystallize,  allowed  to  cool,  and  the  mother  liquor  ex- 
tracted from  the  crystals  in  a  centrifuge  by  centrifugal  force. 

Sugar  is  prepared  from  sugar  cane  in  essentially  the  same  way. 
The  juice  is  squeezed  out  by  passing  the  cane  between  heavy 
rollers,  instead  of  being  extracted  by  diffusion.  The  pressed  cane 
is  termed  bagasse.  The  sugar  is  sent  to  a  refinery  for  further 
purification. 

Syrup  is  prepared  from  sorghum,  sugar  cane,  or  maple  sap  by 
evaporating  the  juice,  usually  in  open  kettles,  with  or  without 
previous  purification  with  lime  and  sulphur. 

Milk  Sugar,  C12H2!,On,  (lactose)  is  not  found  in  plants,  but 
occurs  in  the  milk  of  animals  to  the  extent  of  3  to  6  per  cent.  It 
remains  in  solution  when  the  casein  and  fat  of  milk  have  been 
separated  (as  occurs  in  the  manufacture  of  cheese),  and  may  be 
prepared  by  evaporating  the  liquid  and  recrystallization  of  the 
product.  It  appears  as  hard  white  crystals  with  a  slightly  sweetish 
taste.  It  is  not  as  easily  soluble  in  water  as  cane  sugar.  It  is 
hydrolyzed  to  d-galactose  and  d-glucose. 


3/o 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Milk  sugar  reduces  Fehling's  solution  and  does  not  ferment 
until  inverted. 

Maltose,  C12H22O1:L,  is  formed  from  starch  by  the  action  of 
diastase,  a  ferment  found  in  sprouting  barley  and  other  seeds,  and 
is  important  in  the  manufacture  of  beer,  alcohol,  and  alcoholic 
beverages  from  starchy  materials.  It  forms  fine,  white  needles, 
is  easily  soluble  in  water,  and  is  hydrolyzed  to  glucose. 

Raffinose  occurs  in  small  quantities  in  sugar  beets,  and  in  barley, 
and  in  considerable  quantities  in  cotton  seed.  It  crystallizes  as 
needles  or  prisms,  is  easily  soluble  in  water  and  methyl  alcohol, 
but  is  scarcely  soluble  in  ordinary  alcohol.  It  does  not  act  upon 
Fehling's  solution.  It  is  first  broken  down  by  hydrolysis  into 
two  reducing  sugars,  fructose  and  melibiose;  the  latter  is  then 
split  up  into  glucose  and  galactose. 

Stachyose  occurs  in  the  tubers  of  stachys  tuberifera.  It  is 
hydrolyzed  to  galactose,  fructose,  and  glucose. 

Starch,  C,6H10O5. — This  is  found  in  the  most  different  organs 
of  plants  in  the  form  of  granules  having  an  organized  structure. 


Fig.  81.—  Starch  granules,  (A)  corn,  (B)  potato,  (C)  wheat, 
(D)  bean.     After  Wiley. 

It  is  one  of  the  first  products  of  the  assimilation  of  carbon 
dioxide,  and  can  be  easily  detected  in  the  chlorophyll  granules  of 
the  leaf.  It  is  transferred  from  the  leaf  in  a  soluble  form,  and 


CONSTITUENTS  OF  PLANTS  3/1 

used  for  the  construction  of  other  plant  substance,  or  stored  up  as 
reserve  material  as  such.  Starch  is  thus  found  abundantly  in 
many  seeds,  roots,  and  tubers,  the  parts  of  the  plant  concerned 
with  new  growth. 

The  starch  granules  vary  in  size  and  structure  according  to 
their  origin.  Potato  starch  appears  mostly  as  oval  granules  with 
an  average  diameter  of  0.07  mm.,  but  it  contains  large  granules. 
Wheat  starch  contains  circular  granules  of  two  sizes,  smaller  than 
0.007  mm-  diameter  and  larger  than  0.2  mm.  with  few  granules 
of  intermediate  size.  The  structure  of  the  granules,  and  their  be- 
havior towards  polarized  light  is  also  different,  so  that  one 
familiar  with  their  appearance  can  easily  identify  starches  of 
different  origin  by  means  of  a  microscopic  examination. 

The  elementary  composition  of  starch  is  represented  by  the 
formula  C6H10O5,  but  its  molecular  formula  is  not  yet  known. 
Many  chemists  hold  that  the  starch  molecule  may  contain  more 
than  loo  carbon  atoms. 

Properties  of  Starch. — Air-dry  starch  contains  10  to  20  per  cent 
water.  By  carefully  drying  at  102-110°  C.,  it  may  be  obtained 
water-free.  In  cold  water  it  is  insoluble.  With  hot  water  the 
granules  swell,  break,  and  form  starch  paste,  a  pasty  solution, 
from  which  a  clear  filtrate  can  be  secured.  By  treating  starch 
for  several  days  with  cold  dilute  mineral  acids,  it  may  be  changed 
into  "soluble  starch,"  which  dissolves  in  hot  water  without  forma- 
tion of  a  paste.  Starch  is  tasteless  and  colorless. 

Starch  is  especially  characterized  by  the  blue  color  it  gives  with 
iodine.  This  is  a  very  delicate  test  for  both  starch  and  iodine. 
Starch  is  used  as  an  indicator  with  volumetric  solutions  contain- 
ing iodine. 

When  heated  with  dilute  mineral  acids  under  proper  conditions, 
starch  is  converted  almost  quantitatively  into  glucose.  As  we 
have  already  seen,  this  property  is  utilized  in  the  manufacture  of 
glucose  and  glucose  syrup  from  starch. 

Under  other  conditions,  dilute  acids  change  starch  into  a 
gummy  substance  termed  "dextrin."  This  occurs  in  some 
mucilages  made  from  starch. 


372  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

When  heated  to  a  temperature  above  120°  C.,  starch  is  changed 
to  dextrin.  This  takes  place  in  the  browning  of  flour,  prepara- 
tion of  toast,  and  some  other  processes  of  cooking. 

When  starch  paste  is  treated  with  malt  (this  is  best  done  at  a 
temperature  of  about  65° ), it  is  converted  into  maltose  and  dextrin, 
and  goes  into  a  solution,  which  may  be  fermented.  Advantage  is 
taken  of  this  property  in  the  manufacture  of  alcohol  or  alcoholic 
beverages  from  materials  containing  starch,  such  as  corn,  rye, 
barley,  etc.  The  grain  is  ground,  heated  with  water,  treated  with 
malt,  and  to  the  aqueous  solution  yeast  is  added  to  cause  fer- 
mentation. If  alcohol  or  whiskey  is  desired,  the  fermented 
material  is  distilled.  The  residue  from  the  treatment  with 
malt  is  dried  and  used  for  cattle  food  (brewers'  grains),  or 
it  may  be  fed  without  drying. 

Malt  is  partly  sprouted  barley,  the  sprouts  being  rubbed  off.  It 
contains  an  enzyme  known  as  diastase,  which  acts  upon  starch  as 
stated  above. 

Manufacture  of  Starch. — Starch  is  made  from  potatoes,  corn, 
arrow-root,  cassava,  and  other  materials  rich  in  it.  The  prepara- 
tion of  starch  from  potatoes  is  a  simple  mechanical  operation. 
The  potatoes  are  washed  and  grated  to  a  pulp  to  break  the  cell 
walls.  The  starch  is  washed  out  of  the  pulped  mass  on  sieves.  It 
is  allowed  to  settle  and  dry.  With  some  other  materials  such 
as  wheat  and  rice,  the  proteids  which  accompany  the  starch  must 
be  brought  into  solution  by  fermentation  or  by  means  of  caustic 
soda. 

Inulin,  C6H10O5,  is  found  dissolved,  in  a  pasty  condition  in 
many  plants  of  the  Compositae  family,  and  in  these  plants  plays 
the  part  that  starch  does  in  most  others.  It  is  obtained  from  the 
dahlia  tubers.  It  is  a  white  powder,  composed  of  small  crystals, 
easily  soluble  in  warm  water,  being  slowly  precipitated  on  cool- 
ing, but  readily  by  alcohol.  It  is  not  colored  by  iodine,  hardly 
affected  by  diastase,  and  is  much  more  easily  hydrolized  by  dilute 
acids  than  starch.  Since  it  yields  only  fructose,  it  is  used  for  the 
preparation  of  pure  fructose. 

Glycogen,    CGH10Or>.    is   a    starch-like   carbohydrate    found    in 


CONSTITUENTS  OF  PLANTS  373 

animals.  From  0.6  to  07  per  cent,  is  found  in  the  muscles,  but 
it  disappears  while  the  animal  is  at  hard  work  or  starving.  It  is 
contained  in  quantity  in  the  liver,  and  is  the  reserve  material 
formed  from  the  excess  of  carbohydrates  for  the  furnishing  of 
sugar  to  the  blood. 

Gums. — Gums  are  found  in  many  vegetable  materials.  They 
often  exude  from  cut  places.  Both  hexoses  and  pentoses  are 
formed  by  fHe  hydrolysis  of  gums.  Some  of  the  gums  are  the 
best  materials  for  the  preparation  of  the  pentose  sugars. 

The  following  are  some  gums  and  the  sugars  they  yield  on 
hydrolysis : 

Gum  arable  yields  galactose  and  arabinose. 

Wood  gum,  extracted  from  wood  by  alkalies. 

Cherry  gum  yields  arabinose. 

Peach  gum  yields  galactose  and  arabinose. 

Barley  gum  yields  galactose  and  xylose. 

Galactan  yields  galactose  and  other  sugars,  and  is  found  in 
leguminous  plants. 

Pectins. — These  are  substances  found  in  fruits  and  some  fleshy 
roots.  They  are  soluble  in  water,  and  precipitated  as  a  jelly-like 
mass  by  alcohol.  When  boiled  sufficiently,  they  jelly  on  cooling. 
If  boiled  too  long,  they  will  not  jell.  Pectins  appear  to  be  closely 
related  to  the  carbohydrates,  or  belong  to  them.  They  are  found 
in  apples,  pears,  quince,  cranberries,  beets,  turnips,  etc. 

Cellulose,  C6H10O5. — Cellulose  is  the  chief  constituent  of  the 
cell  walls  of  plants.  It  is  insoluble  in  warm  dilute  acids  or 
alkalies.  In  young  parts  of  plants,  the  cell  walls  are  composed 
of  almost  pure  cellulose.  In  older  organs  the  cellulose  is  inter- 
penetrated with  "incrusting  material."  Cellulose  is  found 
abundantly  in  wood  tissue  and  woody  tissue  of  all  kinds.  Cotton 
is  almost  pure  cellulose.  Flax  and  hemp  are  composed  largely  of 
cellulose.  It  may  be  prepared  by  treating  the  material  successively 
with  ether,  boiling  dilute  acid,  boiling  dilute  alkali,  and  then  with 
cold  dilute  nitric  acid  and  potassium  chlorate  to  remove  the  in- 
crusting  material.  The  residue  consists  of  cellulose.  Cellulose  is 
a  colorless  insoluble  material.  Its  molecular  weight  is  unknown 


3/4  PRINCIPLES  OF  AGRICULTURAL,  CHEMISTRY 

Cellulose  may  be  dissolved  in  a  solution  of  copper  oxide  in  am- 
monia. It  also  dissolves  in  concentrated  sulphuric  acid.  If  the 
solution  is  immediately  diluted  with  water,  a  jelly-like  mass  is 
precipitated.  If  digested  for  some  time  with  the  acid,  and  the 
solution  then  diluted  and  boiled  for  some  time,  sugar  is  produced. 
The  product  is  glucose  from  cotton  and  many  other  celluloses, 
but  d-mannose  is  secured  from  some  other  celluloses,  such  as 
those  from  the  coffee  bean  and  sesame  seed.  The  function  of 
cellulose  in  plants  is  to  form  the  structure  of  plant  cells.  In  seeds 
it  acts  as  a  reserve  material.  Digested  cellulose  appears  to  be 
equal  in  value  to  other  carbohydrates.  Cellulose  contains  44.4 
per  cent,  carbon. 

Lignin. — This  is  the  term  applied  to  the  incrusting  substances 
which  accompanies  the  cellulose  in  wood  and  woody  cells.  Crude 
fiber  is  largely  composed  of  this  mixture  or,  perhaps  compounded 
of  cellulose  and  lignins.  The  chemical  nature  of  the  lignins  is 
not  clearly  known.  They  do  not  appear  to  belong  to  the  group 
of  carbohydrates,  but  contain  55-60  per  cent,  carbon.  Cutin  con- 
tains 68-70  per  cent,  carbon. 

The  quantity  of  lignins  in  the  plant  increases  with  the  age  of 
the  plant  tissue.  Young  woody  tissue  may  contain  little  lignin, 
while  old  woody  tissue  may  be  composed  largely  of  it.  The 
greater  the  quantity  of  lignin  in  the  material,  the  lower  its  value 
for  feeding  purposes. 

Hemicelluloses. — This  term  has  been  proposed  for  the  carbo- 
hydrates of  the  cell  walls  which  are  insoluble  in  water,  but,  un- 
like cellulose,  are  brought  in  solution  by  dilute  acids  or  alkalies. 
Such  carbohydrates  are  of  extensive  occurrence.  The  sugars  pro- 
duced by  their  hydrolysis  are  both  pentoses  and  hexoses. 
Hydrated  celluloses,  formed  by  the  union  of  cellulose  with  water, 
are  largely  dissolved  by  acids  or  alkalies,  and  hence  would  be 
classed  with  the  hemicelluloses. 

Pentosans. — Pentosans  may  be  defined  as  carbohydrates  insol- 
uble in  water,  which  yield  pentose  sugars  on  hydrolysis.  The 
reaction  resulting  in  the  formation  of  furfural  when  pentosans 
are  boiled  with  strong  acids,  is  used  for  their  estimation.  The 


CONSTITUENTS  OF  PLAX'i- 


375 


pentosans  are  accompanied  with  a  substance1  which  yields  a  fur- 
fural-like product,  but  which  product  decomposes  on  standing 
and  does  not  distil  with  the  furfural  a  second  time.  Pentosans 
occur  in  most  plant  materials,  and  are  particularly  abundant  in 
hays  and  straws.  The  pentosans  are  chiefly  gums,  pectins,  and 
hemicelluloses,  though  a  certain  quantity  is  always  found  in  the 
crude  fiber. 

Digested  pentosans  appear  to  be  of  considerable  value  to  the 
animal.  Although  it  is  possible  that  they  have  the  same  value 
as  starch,  when  once  digested,  yet  the  digested  portion  of  feed- 
ing stuffs  rich  in  pentosans  has  a  decidedly  lower  value  for  pro- 
ductive purposes  than  that  of  starchy  materials.  This  appears 
to  be  due  in  part  to  the  labor  of  chewing  the  crude  fiber  of  such 
materials,  but  the  labor  of  chewing  does  not  account  for  the 
entire  deficit. 

The  following  table  shows  the  relative  occurrence  of  these 
classes  of  substances  in  different  materials.2 

NITROGEN-FREE  EXTRACT  OF  SOME  FEEDING  STUFFS. 


i 

*er  cent,  on 

dry  matte 

r 

Simple 
sugars 

Compound 
sugars 

Pentosans 

Residues 

4O7 

TO  71 

16  88 

•y/ 

I  A2 

•66 

O  A  7 

ly.  /i 

4'JC 

21  4O 

l.q* 

=;  66 

•60 

6  81 

CO    2O 

Porn 

I   76 

oil 

522 

i  81 

95:7 

29  81 

O  22 

IO  7^ 

6  76 

54.6 

Crude  Fiber.3 — The  organic  residue  left  after  extraction  of 
plant  substance  with  ether  and  boiling  it  successively  with  i% 
per  cent,  acid  and  alkali,  is  termed  crude  fiber.  The  process  is 
arbitrary,  and  the  object  in  view  when  it  was  devised  was  to  se- 
cure a  product  as  free  as  possible  from  nitrogen. 

1  N.  C.  Bulletin,  No.  178. 

2  Fraps,  Jour.  Am.  Chem.  Soc.,  1900,  p.  543. 

3  See  Tollens,  Exp.  Sta.  Record  8,  p.  649. 


3/6  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Crude  fiber  consists  of  cellulose,  lignin,  cutin,  pentosans,  and 
other  substances.  Digested  crude  fiber  appears  to  be  equally 
as  good  as  starch,  but  the  labor  of  chewing  materials  containing 
much  crude  fiber,  largely  counteracts  the  value  of  the  food. 

Seeds  and  tubers  contain  little  crude  fiber.  Hay,  straw,  chaff, 
and  woody  materials  in  general  may  contain  considerable  quan- 
tities. For  the  crude  fiber  content  of  some  materials,  see  the 
tables  of  analyses. 

About  20  per  cent,  of  the  pentosans  of  hays  and  straws  is  in 
the  crude  fiber,  making  up  10  to  15  per  cent,  of  the  crude  fiber. 


1 

Total 
pentosan 

Pentosan  in 
crude  fiber 

24.86 
26.25 
2O.OO 

5-15 
4-35 
5o6 

Organic  Acids. — Organic  acids  are  found  in  plants  and  plant 
products,  though  often  in  very  small  quantities.  They  may  be 
present  in  the  free  state,  but  are  usually  present  as  salts  of  lime 
or  potash.  In  green  plants  the  acids  are  found  mainly  in  solu- 
tion in  the  sap ;  later  on  they  are  deposited  into  the  cell  tissues. 

The  quantity  of  organic  acids  in  ordinary  agricultural  plants 
is  very  small.  Appreciable  amounts  are  found  in  fruits  and  some 
vegetables.  Tartaric  acid  occurs  in  appreciable  amounts  in 
grapes,  and  is  deposited  as  potassium  acid  tartrate  in  wine. 
Small  amounts  are  found  in  pineapples,  cucumbers,  and  tomatoes. 
Malic  acid  occurs  in  apples,  from  which  it  gets  its  name,  but  is 
widely  distributed,  occurring  in  a  number  of  fruits  and  vegetables. 
Oxalic  acid  and  succinic  acid  are  found  in  many  plants. 

Citric  acid  is  present  in  lemons  and  limes,  and  in  small  amounts 
in  pears,  beans,  cherries,  and  other  fruits.  Tannic  acid  is  not 
present  in  food  plants  to  appreciable  extent,  though  it  is  found 
in  tea  and  coffee.  It  is  used  for  tanning  leather.  Some  plants 
are  grown  for  the  tannic  acid  they  contain. 

Lactic  acid  occurs  in  silage  and  sour  milk. 

The  organic  acids  have  little  food  value,  but  affect  the  palat- 


CONSTITUENTS  OF  PLANTS  377 

ability  of  the  food,  and  perhaps  exert  a  favorable  influence  upon 
digestion  by  stimulating  the  secretion  and  flow  of  the  digestive 
juices. 

Essential  Oils. — The  characteristic  flavor  and  odor  of  many 
plant  products  are  due  to  volatile  compounds  known  as  essential 
oils.  Turpentine,  peppermint  oil,  oil  of  roses,  and  oil  of  lemon 
are  examples  of  essential  oils.  Spices,  flavoring  extracts,  condi- 
ments and  appetizers  in  general,  flowers,  and  certain  fruits  are 
characterized  for  the  most  part  by  the  presence  of  essential  oils. 
Hays  owe  a  portion  of  their  odor  and  flavor  to  essential  oils. 
Rape,  turnips,  cabbage,  and  parsley  contain  essential  oils.  Some 
of  the  essential  oils  impart  palatability  to  the  food,  and  stimulate 
the  secretion  and  flow  of  the  digestive  juices.  While 
of  little  or  no  value  for  the  production  of  muscle  or  energy,  they 
aid  the  appetite  of  the  animal. 

Certain  feeds  containing  essential  oils  are  undesirable  for  milch 
cows,  as  they  impart  a  disagreeable  flavor  to  the  milk.  Garlic, 
wild  onions,  and  rape  are  examples  of  these. 

Organic  Phosphorus  Compounds. — Plants  also  contain  organic 
phosphorus  compounds,  chief  among  which  is  phytin,1  which  may 
be  decomposed  into  inosite  and  phosphoric  acid.  This  substance 
is  found  especially  in  wheat  bran,  rice  bran,  and  cottonseed  meal. 
Other  organic  phosphorus  compounds  are  present. 

Heat  Value. — The  energy  of  a  feed  or  nutrient  is  measured  by 
the  heat  which  it  produces  when  burned.  The  unit  of  heat  is  the 
calorie,  written  c.,  which  is  the  amount  of  heat  required  to  raise 
the  temperature  of  I  gram  water  i°  Centigrade.  The  large 
calorie  (C)  is  1,000  c,  and  the  therm  (T)  is  1,000  C.  Several 
kinds  of  calorimeters  are  used.  In  the  bomb  calorimeter,  the 
material  is  placed  in  a  platinum  capsule  in  an  iron  vessel,  lined 
with  platinum  or  enamel.  The  bomb  is  filled  with  oxygen  under 
high  pressure,  and  placed  in  a  vessel  of  water  with  a  stirrer,  and 
thermometer,  and  properly  insulated  to  decrease  heat  changes. 
The  material  is  ignited  by  means  of  an  electric  current  which 
heats  a  small  piece  of  iron  wire,  and  the  rise  in  temperature  of 
the  water  is  ascertained.  Knowing  the  amount  of  heat  required  to 
1  N.  Y.  (Geneva)  Bull.  250;  Texas  Bull.  156. 
25 


378 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


heat  the  apparatus,  the  quantity  of  water,  the  rise  in  temperature, 
and  the  loss  of  heat  by  radiation,  the  amount  of  heat  produced 
by  the  known  weight  of  substance  may  be  ascertained.  Urine  is 


Fig.  82. — Calorimeter  (Atwater  and  Hempel)  in  which  the  substance 
is  burned  in  compressed  oxygen. 

either  evaporated  in  a  vacuum  directly,  or  absorbed  in  paper  of 
known  heat  value,  and  then  dried.  Heat  measurements  are  made 
very  often  in  investigations  of  animal  nutrition.1 

1  For  discussion  of  heat  values  of  nutrients,  see  Stohinann,  Exp.     Sta. 
Record  No.  6,  p.  590. 


CHAPTER  XVIII. 


COMPOSITION  OF  PLANTS  AND  FEEDS. 

Feeding  stuffs  are  divided  into  two  great  groups — concentrates 
and  roughages.  A  concentrate,  or  concentrated  feeding  stuff, 
consists  of  seeds,  and  various  milling  by-products.  A  concen- 
trate is  rich  in  protein  or  in  nitrogen-free  extract  and  contains 
comparatively  small  amounts  of  crude  fiber.  As  a  general  rule, 
the  crude  fiber  of  a  concentrated  feed  does  not  exceed  10  per 
cent.,  though  there  are  exceptions;  crushed  cottonseed  cake,  for 
example,  contains  about  27  per  cent.  Examples  of  con- 
centrates are  corn,  wheat,  rice  bran,  cottonseed  meal,  gluten 
meal,  wheat  bran,  etc. 

A  roughage  is  a  feed  containing  relatively  high  percentages  of 
crude  fiber  and  much  smaller  amounts  of  nitrogen-free  extract 
and  protein.  Further,  the  constituents  of  the  nitrogen-free  ex- 
tract are  less  digestible  and  less  valuable  to  the  animal  than  those 
of  concentrates. 

Seeds. — The  seed  contains  an  embryo  plant  with  sufficient  plant 
food  and  organic  matter  to  give  the  young  plant  a  good  start  in 
life.  Seeds  of  agricultural  importance  may  be  divided  into  three 
classes : 

(a)  Starchy  Seeds. — Seeds  of  the  cereals  belong  to  this  group. 

(b)  Oily    Seeds. — Seeds    of    cotton,    flax,    hemp,    sunflower, 
mustard,  etc.,  belong  in  this  group.     OH  is  manufactured  from 
them. 

(c)  Seeds  Rich  in  Protein. — Seeds  of  peas,  beans,  and  other 
leguminous  crops  belong  in  this  group. 

Other  classes  of  seeds  are  known,  but  they  are  not  of  great 
agricultural  importance. 

Germination. — In  germination,  the  reserve  material  in  the  seed 
is  converted  into  soluble  forms,  conveyed  into  the  growing  plant, 
and  formed  into  new  material.  The  chemistry  of  this  change 
depends  to  some  extent  upon  conditions.  The  proteids  are  con- 
verted into  asparagin  and  other  amido  bodies,  and  the  fat  is 
oxidized  and  changed  to  soluble  materials,  which  are  used  by  the 


380  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

plant.  The  reserve  carbohydrates  undergo  changes  similar  to 
the  fat.  In  some  seeds,  as  in  barley,  ferments  are  formed  which 
change  starch  into  sugar. 

The  change  in  composition  of  seeds  on  sprouting  may  be 
studied  by  allowing  a  weighed  quantity  of  seed  to  sprout  in  the 
dark,  and  determining  the  constituents  of  the  original  seed,  and 
of  the  sprouted  seed.  The  sprouting  must  take  place  in  the 
dark,  since  when  light  is  present  carbon  dioxide  is  assimilated 
and  masks  the  change. 

Composition  of  Plants  at  Different  States  of  Growth . — Plants  do 
not  have  the  same  composition  at  different  stages  of  growth.  The 
plant  increases  in  weight  up  to  maturity.  In  the  earlier  part  of 
the  life  of  the  plant,  nitrogenous  material  is  taken  up  more 
rapidly.  Before  the  formation  of  fruit,  the  reserve  material  pro- 
duced is  stored  up  in  leaves,  stem,  roots,  or  tubers.  At  the  time 
of  fruiting,  this  reserve  passes  into  the  seed.  During  the  later 
stages  of  plant  growth,  lignification  of  the  tissues  takes  place. 
That  is  to  say,  the  cellular  material  becomes  penetrated  with 
lignin  and  the  stems,  etc.,  become  more  woody  and  difficult  to 
digest. 

The  composition  of  plants  at  different  stages  of  growth  mav 
be  studied  in  two  ways. 

The  first  method  consists  in  selecting  and  analyzing  averagt 
specimens  of  the  plant  at  the  desired  periods  of  growth.  This 
method  of  experiment  shows  the  change  in  the  individual  plant. 

The  second  method  consists  in  harvesting  definite  areas  of  the 
same  field  when  the  field  has  reached  the  average  condition  de- 
sired and  subjecting  samples  to  analysis.  This  method  represents 
the  production  of  the  field  at  different  stages  of  growth.  The 
plants  harvested  are  not  all  in  the  same  condition  of  growth. 
This  method  is  better  suited  for  small  plants  and  grasses  than  the 
first  method.  Both  methods  are  open  to  error,  as  there  may  be 
differences  in  the  soil  or  in  the  individual  development  of  differ- 
ent plants. 

The  general  results  of  these  experiments  are  as  follows : 

The  water  in  the  green  plant  decreases  with  the  age  of  the 


COMPOSITION   OF   PLANTS   AND   FEEDS 


plant.  In  order  to  eliminate  the  effect  of  this  variation,  the  per- 
centages of  other  constituents  of  the  plant  should  be  calculated 
to  percentages  of  the  water-free  substance,  or  dry  matter  of  the 
plant.  The  statements  below  refer  to  the  composition  of  the  dry 
matter. 

The  percentage  of  ash  usually  decreases  with  the  age  of  the 
plant.  That  is,  the  production  of  organic  matter  takes  place 
more  rapidly  than  the  withdrawal  of  ash  material  from  the  soil. 

The  percentage  of  protein  decreases  decidedly.  In  some  cases 
the  percentages  when  the  seed  are  nearly  ripe  are  only  about  half 
those  at  the  beginning  of  growth.  The  protein,  however,  consists 
largely  of  amides  or  amido  compounds  in  the  early  stages  of  the 
plant's  life,  and  these  amides  have  little  or  no  value  for  the  pro- 

COMPOSITION  OF  SOME  PLANTS  AT  DIFFERENT  STAGES  OF  GROWTH. 


Water-free 

Water 

Nitro- 

Ash 

Protein 

Fiber 

gen-free 

Fat 

extract 

Corn 

88  6l 

8.5 

17.2 

26.0 

45-1 

3-2 

uiy  2-2  

85.76 

8.0 

14.4 

27.3 

47-6 

2-7 

August    5,  tasseled  

84.64 
82.08 
8l.I5 

5-9 

5.7 
4-7 

II.8 
II.  2 
8.9 

26.4 
24.1 
24.3 

53-6 
56.9 
60.3 

2.3 

2.1 

1.8 

0                        K           - 

76.81 

4.2 

9.2 

20.9 

63-  1 

2.6 

Timothy 

June  23,  nearly  headed-  • 

78.70 

7-5 

II.  O 

28.7 

49.0 

3-8 

Julv    3,  full  bloom  '   7J-92 

6.1 

8-3 

33.3 

49-3 

3>o 

July  14,  out  of  bloom  •  ..|   65.70 

5-2 

5-7 

34-7 

51-7 

2-7 

Julv  30,  nearly  ripe  

63.27 

5-° 

5-5 

37-1 

50.2 

2.2 

Kentucky  Blue  Grass 
April  28,  3  to  6  inches... 

68.05 
66  71 

ii.  5 

TO.  7 

18.0 
M-5 

22.2 

22.7 

42.7 
48.9 

5.6 
4.2 

MayiS,  panicles  spread- 

63.3 

8.7 

II.  I 

24-4 

51-9 

3-9 

May  28,  early  bloom  
June  7,  after  bloom  

j  o 
62.91 
'   61.24 
1   51-67 

8.5 

8.7 

IO.O 

9-7 
7-9 
7-9 

29.1 
29.9 

3°-5 

50.5 
51-8 
48.5 

2.2 
2-7 
3'1 

Red  Clover 

61.21 
47-13 

8-3 

7-7 

14-3 
13-5 

27.8 
27.8 

47-9 
48.6 

1-7 

2.4 

382  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

duction  of  flesh.  As  the  plants  approach  maturity,  the  per- 
centages of  non-proteid  nitrogen  decreases. 

The  fat  is  irregular,  though  it  shows  a  tendency  to  decrease. 
The  crude  fiber  increases  with  most  plants.  Indian  corn  is  an 
exception,  since  the  production  of  a  large  quantity  of  starchy 
seed  decreases  the  percentage  of  fiber.  The  nitrogen- free  extract 
usually  increases,  though  the  changes  are  somewhat  irregular. 
The  digestibility  decreases. 

The  total  quantity  of  dry  matter  per  acre  appears  to  increase 
during  the  entire  period  of  growth.  In  the  latter  stages  of 
maturity  of  the  plant,  the  increase  is  largely  made  up  of  crude 
fiber. 

Some  analyses  of  plants  at  different  stages  of  growth  are  shown 
in  the  table  .-1 

Time  of  Harvest. — The  best  time  to  harvest  depends  on  the 
kind  of  plant  and  the  purpose  for  which  it  is  grown,  as  well  as  on 
the  weather  of  the  harvesting  period. 

Suppose  hay  is  grown  for  market.  The  object  then  is  to  secure 
the  largest  possible  quantity  of  hay  of  the  highest  market  value. 
A  large  quantity  of  low  grade  hay  may,  or  may  not,  be  more 
profitable  than  a  smaller  quantity  of  high  grade  hay. 

Suppose  hay  is  grown  for  feed.  The  object  is  then  to  get  the 
largest  possible  amount  of  digestible  nutrients  per  acre.  The  best 
period  of  harvest  for  this  purpose  is  when  the  plant  is  in  full 
bloom. 

Suppose  the  clover  or  grass  is  grown  for  seed.  Then  the  object 
is  to  produce  the  most  seed  of  the  best  quality.  The  seed  must 
be  well  matured,  but  at  the  same  time  the  harvest  must  not  be  so 
late  that  any  considerable  quantity  is  lost  by  shattering. 

Other  Factors  which  Influence  Composition. — Other  factors 
which  influence  the  composition  of  crops  are  the  seed,  the  soil, 
climate,  and  method  of  preparation  or  preservation. 

The  composition  and  individuality  of  the  seed  influence  the 
composition  and  size  of  the  plant.  In  many  cases,  the  heavier 
1  Compiled  from  Bulletin  n,  Office  Exp.  Station,  U.  S.  Dept.  Agr. 


COMPOSITION   OF   PLANTS   AND   FEEDS  383 

the  seed,  the  more  vigorous  the  young  plant.  The  larger  seed,  of 
course,  contain  more  reserve  material  and  plant  food. 

Selection  of  seed  from  individuals  of  a  desired  type  may  affect 
the  composition  of  the  plant.  Thus,  at  the  Illinois  Station,  corn 
of  high  and  low  protein  and  high  and  low  fat  have  been  produced. 
By  selecting  seeds  from  beets  containing  high  quantities  of  sugar, 
the  sugar  content  of  the  sugar  beet  has  been  increased  8  to  10 
per  cent.  It  is  not  possible  to  improve  all  crops  in  this  way. 

The  soil  affects  the  composition  of  the  crops  to  some  extent. 
Foliage  crops  grown  upon  rich  soils  contain  a  larger  percentage 
of  nitrogen  than  those  grown  on  soils  poor  in  nitrogen.  Leaves 
and  stems  are  influenced  to  a  greater  extent  than  seed  by  the  soil, 
because  the  seed  are  more  constant  in  composition.  Wheat  and 
other  grains  show  material  differences  in  composition  when  grown 
upon  different  soils.  Not  all  plants  are  affected  by  the  composi- 
tion of  the  soil.  Lawes  and  Gilbert  found  that  the  use  of  nitro- 
genous and  mineral  manures  for  twenty  years  did  not  affect  the 
nitrogenous  content  of  wheat. 

As  the  plant  contains  more  nitrogen  during  early  stages  of 
growth,  anything  which  cuts  short  the  growing  season  will  cause 
the  crop  to  contain  slightly  more  nitrogenous  material.  If  the 
growth  of  the  plant  is  checked  at  the  time  of  seed  formation, 
shrunken  or  immature  seed  may  result.  Such  grain  contains  less 
starch  and  more  nitrogenous  compounds  than  those  fully  matured. 
Plants  grown  in  arid  or  semi-arid  regions  may  contain  a  higher 
percentage  of  nitrogen  than  in  regions  of  more  abundant  rainfall. 
For  instance,  the  nitrogen  content  of  Texas  cottonseed  meal1  is 
considerably  greater  in  the  western  or  semi-arid  part  of  the  state 
than  in  the  eastern  part. 

Hay  and  Hay  Making. — Hay  is  the  dried  and  partly  fermented 
leaves  and  stems  of  certain  grasses  and  clovers.  Some  fermenta- 
tion is  requisite  to  develop  the  characteristic  flavor  and  aroma. 
The  method  used  for  hay  making  depends  on  the  character  of  the 
plant  and  the  climate.  A  succulent  plant  and  a  moist  climate 
demands  more  care  than  dryer  plants  and  a  dry  climate.  Some 
1  Texas  Bulletin,  70. 


384  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

plants,  such  as  cowpeas,  are  difficult  to  cure  on  account  of  the 
large  succulent  vines,  which  remain  moist  after  the  leaves  have 
become  dry  and  so  brittle  that  they  break  off.  For  a  similar  rea- 
son alfalfa  also  is  difficult  to  cure  .  Often  alfalfa  hay  consists 
entirely  of  stems. 

The  Arkansas  Experiment  Station  found  that  young  or  vigor- 
ously growing  vines  of  cowpeas  very  difficult  to  cure  even 
under  favorable  weather  conditions,  while  mature  vines  cured 
with  little  difficulty  in  favorable  weather,  and  usually  made  good 
hay  even  after  an  exposure  to  rain  and  cloudiness  from  two  to 
four*  days. 

In  hay  making  the  plants  are  usually  cut  and  allowed  to  lie  ex- 
posed to  the  sun  all  day;  then  raked  or  piled  into  heaps  more  or 
less  loose,  for  further  curing,  and  finally  piled  into  larger  heaps, 
or  taken  to  the  barn.  If  the  large  heaps  are  formed  while  the 
material  is  too  moist,  excessive  fermentation  will  take  place, 
which  in  some  cases  has  gone  so  far  as  set  fire  to  the  stack.  In 
Wisconsin,  Short  found  that  by  leaving  hay  out  four  days  after 
cutting,  during  which  time  there  was  a  rain,  there  was  a  loss  of 
over  4^2  per  cent,  dry  matter  and  3^2  per  cent,  protein.  Six 
weeks  later  nearly  one-fourth  of  the  dry  matter  and  protein  dis- 
appeared. 

Emmerling  left  grass  exposed  for  18  days,  during  nine  of  which 
rain  fell,  with  the  results  given  in  the  following  table : 

PERCENTAGE  Loss  OF  INGREDIENTS  OF  HAY  IN  EXPOSURE  TO  RAIN. 


In  cocks 

In  swaths 

Dry  matter  

I8.3 
31.0 
29.0 
19.8 

29.4 
41.0 
24.8 
38.8 

Fat  

Even  without  rain,  when  the  process  of  drying  is  slow,  a  loss 
takes  place  due  to  the  respiration  of  the  living  tissues,  by  which 
protein  is  decomposed  or  non-proteins  oxidized.  The  loss  has 
been  as  much  as  12  per  cent,  dry  matter  in  10  days  with  young 


COMPOSITION   OF   PLANTS  AND   FEEDS  385 

Silage. — Silage  is  a  feeding-stuff  preserved  in  a  moist  condi- 
tion. It  is  made  by  placing  the  finely  chopped  material  in  an  air 
tight  receptable.  More  or  less  fermentation  takes  place,1  which 
destroys  sugar,  produces  acids,  and  causes  the  loss  of  ten  or  twelve, 
per  cent,  substance.  The  acidity  of  the  silage  depends  upon  the 
conditions  of  preparation.  If  a  silo  is  filled  rapidly,  the  mass 
weighted  down  and  the  air  excluded  as  much  as  possible,  a  slow 
fermentation  takes  place  caused  by  bacteria,  which  results  in  a 
very  acid  product,  termed  sour  silage.  It  may  contain  0.6  to  1.6 
per  cent.  acid.  If  the  material  is  put  in  slowly  and  loosely,  a 
preliminary  rapid  fermentation  takes  place  which  heats  the  mass, 
destroys  the  acid-forming  bacteria,  and  excludes  air.  Fermenta- 
tion then  goes  on  more  slowly,  producing  a  sweet  silage.  Too 
high  a  temperature  would  produce  bad  results.  Sweet  silage  is 
said  to  become  moldy  on  exposure  to  the  air,  while  acid  silage  is 
relatively  resistant  to  decay.  The  changes  are  due  to  the  living 
cell,  and  enzymes  of  the  plant,  as  well  as  to  bacteria. 

The  following  experiment  shows  the  effect  of  temperature  on 
the  silage.  The  volatile  acid  is  chiefly  acetic  acid,  the  non- 
volatile is  lactic. 


Temperature  of  formation 

Volatile  acid 
Per  cent. 

Non-volatile 
acid.  Percent. 

Below  32°  C  

o  62  to  i  s6 

->2  to  49°  C 

56  to  70°  C-  • 

The  fermentation  also  converts  some  of  the  proteid  nitrogen 
into  non-proteids,  the  action  going  so  far  as  even  to  form  a  small 
quantity  of  ammonia. 

A  silo  must  be  perfectly  air-tight,  or  the  loss  resulting  will  be 
great ;  the  walls  must  be  rigid,  the  inner  surface  must  be  smooth 
and  uniform,  and  it  should  dry  out  quickly  and  completely. 

Losses  in  Silage  Making. — The  loss  in  a  silo  depends  upon  its 
construction,  on  the  crop  siloed,  and  on  the  amount  of  moisture 
present.  The  loss  is  much  lessened  by  proper  construction  of  the 
1  Bulletin  70,  Connecticut  Station. 


386  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

silo.     The  amount  of  moisture  present  in  the  crop  had  the  follow- 
ing effect  in  one  experiment : 

Moisture,  per  cent.  Loss,  per  cent. 

71.67 8.63 

74.61  10.01 

80.66 16.66 

An  excess  of  moisture  thus  causes  a  greater  loss.  Water  is 
sometimes  added  to  crops  siloed  when  they  do  not  contain  enough 
water  to  make  good  silage. 

As  regards  the  nature  of  the  crop,  King  found  the  necessary 
loss  for  corn  to  be  5  to  10  per  cent.,  and  for  clover  10  to  18  per 
cent.  Corn  well  matured  and  in  good  condition  for  shocking,  but 
with  leaves  still  green,  is  in  the  proper  stage  for  silage.  Silage 
from  immature  fodder  is  more  acid  than  that  from  more  mature 
plants. 

Feed  Laws. — Many  of  the  States  have  laws  regulating  the  sale 
of  concentrated  commercial  feeding  stuffs.  The  laws  usually  re- 
quire the  feed  to  be  true  to  name,  and  prohibit  the  sale  of  un- 
wholesome feed.  A  guaranteed  analysis  is  usually  required,  but 
some  states  require  a  guarantee  of  protein  and  fat  only,  others 
require  crude  fiber  in  addition  to  protein  and  fat,  and  still  others 
require  a  guarantee  of  nitrogen-free  extract  in  addition  to  the 
others.  A  guarantee  of  protein  and  fat  is  not  sufficient  to  show 
the  quality  of  the  feed,  and  laws  which  require  only  such  guar- 
antee cannot  be  considered  to  provide  sufficient  protection. 

It  is  not  sufficient  that  the  feed  should  come  up  to  the  guar- 
anteed analysis,  but  it  should  be  composed  of  the  ingredients 
claimed,  and  no  one  should  purchase  a  feed  without  knowing  the 
feeding  stuffs  present.  It  is  possible  to  make  up  the  guaranteed 
analysis  by  means  of  substances  of  high  composition  but  of  low 
digestibility  and  low  feeding  value.  Mixed  feeds  are  often  put 
on  the  market  which  contain  ingredients  that  could  not  be  readily 
sold  separately,  and  are  often  sold  at  prices  far  in  excess  of  their 
real  feeding  value. 

The  guaranteed  analysis  of  a  feeding  stuff  must,  therefore,  be 
regarded  as  a  guarantee  of  the  quality  of  the  particular  feed 
claimed  to  be  sold.  The  fact  that  the  feed  comes  up  to  the 


COMPOSITION   OF   PLANTS  AND  FEEDS  387 

guaranteed  analysis  is  not  necessarily  proof  that  the  feed  is  com- 
posed of  the  ingredients  named,  but  the  feed  should  be  examined 
microscopically  or  otherwise  when  necessary.  Two  feeds  of  the 
same  guaranteed  analysis  do  not  necessarily  have  the  same  feed- 
ing value,  unless  they  are  the  same  feed.  A  feed  should  be 
true  to  name,  regardless  of  the  guarantee.  If  foreign  matter  has 
been  mixed  with  it,  the  feed  is  adulterated,  regardless  of  the 
chemical  analysis.  Feeds  are  sometimes  adulterated  with  other 
by-products  of  the  same  process  of  manufacture.  Wheat  bran 
may  be  adulterated  with  screenings;  cottonseed  meal  may  have 
such  a  quantity  of  hulls  left  in  it  that  it  is  no  longer  entitled  to  be 
called  cottonseed  meal;  an  excess  of  hulls  may  be  run  into  rice 
bran. 

The  term  feeding  stuff  does  not  include  indigestible  materials, 
such  as  peat,  earth,  ground  leather,  sand,  etc.,  or  poisonous 
materials,  such  as  poisonous  plants,  poppy  seeds,  castor-oil  seed 
meal,  etc.  The  value  of  a  feed  depends  upon  its  nature  and  its 
chemical  analysis.  Chemical  analysis  alone  is  not  sufficient,  since 
materials  vary  considerably  in  digestibility  and  nutritive  value, 
even  with  the  same  chemical  composition.  A  microscopic  ex- 
amination is  also  necessary. 

Injurious  Feeds. — Rust  and  smut  fungi  sometimes  cause  disease 
or  injury  to  animals  eating  the  diseased  feed.  Moldy  feed  is 
liable  to  be  dangerous  to  animals,  as  poisonous  substances  may 
be  present.  Yeasts  found  in  by-products  from  beverages,  etc., 
cause  fermentation  in  the  stomach.  Boiling  or  steaming  will 
obviate  such  danger.  Frozen  fodder  feed  in  quantity  is  liable  to 
cause  digestive  disturbances.  When  it  thaws,  it  readily  decom- 
poses. Many  kinds  of  weed  seeds,  such  as  field  poppy,  and  corn 
cockles,  have  injurious  effects.  Sand,  dirt,  and  ashes  may  cause 
no  injury,  but  sometimes  they  give  rise  to  serious  digestive  dis- 
turbances, constipation,  or  even  death. 

Percentage  of  Water. — The  quantity  of  water  in  feeds,  etc., 
may  be  seen  on  reference  to  the  tables.  Hay  and  straw  contain 
12-17  Per  cent->  cereal  grains  11  to  15  per  cent,  and  oil  cake  and 
meal  contains  6  to  13  per  cent.  Meals,  cakes,  and  grain  easily 


388 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


undergo  decomposition  if  they  contain  more  than  14  per  cent, 
water. 

Preparation  of  Feeds. — Crushing  or  grinding  the  grain  is  often 
of  advantage,  especially  for  certain  kinds  of  animals,  or  for  those 
with  defective  teeth,  when  the  grain  is  small  or  hard.  The  fol- 
lowing shows  the  effect  of  feeding  oats  to  horses,  with  chopped 
hay: 

Per  cent, 
dry  matter  digested 

Whole  oats 64.6 

Crushed  oats 68.6 

Coarse  ground  oats 72.7 

Corn,  rye,  buckwheat,  Kafir  corn,  milo  maize,  and  leguminous 

seed,  should  best  be  ground  for  all  animals.     The  following  are 

some  differences: 


Dry  matter  digested 

Horses 

Pigs 

per  cent. 

82.5 
89-5 

per  cent. 

74-4 
88.4 

In  a  number  of  experiments  with  pigs,  the  effect  of  grinding 
the  corn  was  to  reduce  by  six  per  cent,  the  quantity  needed  for 
the  same  gain  in  weight.  Moistening  the  feed  prevents  its  being 
blown  away  and  prevents  the  fine  particles  of  meal  from  getting 
in  the  eyes  or  lungs.  Cooking,  scalding,  or  steaming  kills  weed 
seeds,  injurious  molds  or  bacteria,  and  animal  parasites,  but  as  a 
rule,  decreases  the  digestibility  of  the  feed.  Cooked  or  steamed 
food,  however,  is  valuable  for  pigs.  The  following  shows  the 
effect  of  cooking: 

Digestibility  of  protein 


Bran 

Hay 

per  rent. 

77  O 

per  cent. 
46  o 

Steamed  •              •    •     •  •         

70  o 

^O  o 

COMPOSITION   OF    PLANTS   AND   FEEDS  389 

Conditions  of  Growth. — The  stage  of  growth,  as  we  have 
already  seen,  affects  the  composition  of  the  plant.  Plants  grown 
wide  apart  give  coarser  fodder  than  those  sown  thickly.  Soil  and 
manures  also  affect  the  nutritive  values  of  plants,  especially  in 
meadows,  where  acidity  or  unfavorable  soil  conditions  may 
promote  the  growth  of  plants  not  well  suited  for  pasturage. 
Liming  and  drainage  may  encourage  growth  of  clovers,  vetches, 
and  sweet  grasses.  Addition  of  nitrogenous  manure  may  cause 
increased  percentages  of  protein.  Weather  conditions  also 
affect  the  quality  of  the  plants.  In  wet  years,  the  plant  grows 
larger  and  is  more  woody.  In  dry  season,  the  plant  is  short  and 
compact. 

Composition  of  Feeding-Stuffs. — The  composition  of  feeding- 
stuffs  shown  in  the  various  publications  represents  the  average  of 
variable  analyses.1  The  average  composition  varies  with  differ- 
ent sections  of  the  country,  and  for  information  in  regard  to  the 
composition  of  local  feeds,  the  student  should  consult  the  re- 
ports and  Bulletins  of  his  State  Experiment  Station.  Reports  of 
Feed  Control  officials  also  show  the  composition  of  concentrated 
feeding  stuffs,  while  the  guaranteed  analyses  are  printed  on  the 
package,  or  a  tag  attached  to  it. 

Concentrates. — The  concentrates  used  in  feeding  are  largely 
by-products  from  the  manufacture  of  various  articles.  These 
feeding  stuffs  may  be  grouped  according  to  their  chemical  com- 
position or  according  to  their  origin.  They  are  distinguished  from 
roughages  by  being  rich  in  protein  or  nitrogen-free  extract,  and 
low  in  crude  fiber. 

Classes  of  Concentrates. — Concentrated  feeds  may  be  arranged 
in  six  groups,  according  to  their  content  of  protein: 

I.  Protein  30  to  50  per  cent. — Cottonseed  meal,  gluten  meal, 
linseed  meal,  dried  distiller's  grains,  peanut  meal. 

II.  Protein  20  to  30  per  cent.— Malt  sprouts,  gluten  feed,  cot- 
tonseed feed,  dried  brewers'  grain,  germ  oil  meal,  whole  pressed 
cottonseed. 

1  Bulletin  11,  Office  Exp.  Sta. 


390  PRINCIPLES  OE  AGRICULTURAL  CHEMISTRY 

III.  Protein  14  to  20  per  cent. — Wheat  middlings,  wheat  bran, 
wheat  shorts,  oat  middlings,  flax  feed,  rye  feed,  cotton  seed,  sun- 
flower seed. 

IV.  Protein  10  to  14  per  cent. — Rice  bran,  rice  polish,  ground 
oats,  ground  wheat,  barley  meal,  rye  meal,   hominy   feed,  oats 
mixed  with  barley. 

V.  Protein  8  to  10  per  cent. — Corn  bran,  corn  meal,  corn  chops, 
corn  and  oat  feed,  oat  feed,  dried  beet  pulp,  beet  molasses,  kaffir 
corn,  milo  maize,  corn  and  cob  meal,  sorghum  seed. 

VI.  Protein  less  than  8  per  cent. — Cane  molasses. 

Classes  of  Roughages. — Roughages  may  be   divided  into   the 
following  groups : 

I.  Fodders. — Corn  fodder,  corn  husks,  katfir  stover,  sorghum. 
These  contain  from  3  to  12  per  cent,  protein  and  from  23  to  35 
per  cent,  crude  fiber. 

II.  Cereal  Straws. — Oat,  barley,  rice,  rye,  and  wheat  straws, 
containing  3  to  6  per  cent,  protein  and  35  to  40  per  cent,  crude 
fiber. 

III.  Grass  Hays. — Bermuda,   Johnson  grass,  timothy,   millet, 
etc.,  containing  5  to  15  per  cent,  protein,  and  22  to  35  per  cent, 
crude  fiber. 

IV.  Legume  Hays. — Alfalfa,  clover,  cowpeas,  peanuts,  vetch, 
etc.,  containing  12  to  20  per  cent,  protein  and  20  to  28  per  cent, 
crude  fiber. 

V.  Waste  Milling  Products. — Peanut  hulls,  corn  cobs,  cotton- 
seed hulls,  oat  chaff,  oat  hulls,  rice  hulls,  wheat  chaff,  etc.,  some- 
times mixed  with  concentrated  feeds,  but  properly  classed  with 
roughage.     They  contain  2.5  to  5  per  cent,  protein  and  30  to  48 
per  cent,  crude  fiber. 

VI.  Fresh   Grass   or  Fodder. — Millet,   oats,  barley,   sorghum, 
timothy,  etc.,  contain  about  80  per  cent,  water  and  I  to  4  per  cent, 
protein. 

VII.  Fresh   Legumes. — Alfalfa,    clover,    cowpea,    vetch,    etc., 
containing  70  to  85  per  cent,  water  and  2.5  to  5  per  cent  protein. 

VIII.  Silage. — Corn,  sorghum,  clover,  usually  corn  containing 
70  to  85  per  cent,  water  and  I  to  4  per  cent,  protein. 


COMPOSITION   OF   PLANTS  AND   FEEDS  391 

IX.  Roots  and  Tubers. — Carrots,  potatoes,  turnips,  beets,  etc., 
containing  70  to  90  per  cent,  water  and  i  to  3  per  cent,  protein. 

Description  of  Concentrates. — A  few  of  these  feeding-stuffs 
will  be  discussed  briefly. 

Cottonseed  Meal  is  prepared  by  cooking  and  pressing  the  ker- 
nels of  cotton  seed.  It  contains  36  to  52  per  cent,  protein,  accord- 
ing to  its  origin  and  freedom  from  hulls.  The  meal  increases  in 
protein  from  the  eastern  part  of  the  country  to  the  west,  being 
richest  in  west  Texas.  The  meal  is  often  adulterated  with  hulls. 
The  quantity  of  hulls  may  be  roughly  estimated  by  deducting  5 
per  cent,  from  the  crude  fiber  and  multiplying  the  remainder  by 
2l/4.  Thus  a  meal  containing  10  per  cent,  crude  fiber  contains 
10-5  x  2^4  =  11.3  per  cent,  hulls,  approximately. 

Brewers'  grains  are  the  dried  residue  from  the  treatment  of 
cereals  with  malt,  for  the  preparation  of  beer. 

Pressed  zvhole  cottonseed  is  made  by  pressing  the  whole 
cotton  seed  between  rollers.  It  thus  contains  all  the  hulls. 

Wheat  bran  is  the  outer  covering  of  the  wheat  grain.  Some- 
times the  screenings,  containing  oats,  weed  seeds,  wheat,  etc.,  are 
mixed  with  the  bran,  with  or  without  grinding.  This  is  not 
allowable  under  most  feed  laws. 

Alfalfa  meal  is  ground  alfalfa.  It  is  properly  a  roughage  and 
not  a  concentrate. 

Rice  bran  is  the  outer  coating  of  the  rice  grain,  including  some 
of  the  germ.  It  contains  about  ten  per  cent,  each  of  protein  and 
fat,  but  is  liable  to  become  rancid. 

Rice  polish  is  obtained  in  polishing  rice.  It  contains  some  of 
the  germ. 

Corn  bran  is  the  outer  covering  of  the  corn  grain. 

Kafir  corn  and  milo  maize  are  similar  to  corn,  but  contain  more 
protein.  They  have  about  10  per  cent,  less  feeding  value  than 
corn. 


CHAPTER  XIX. 


DIGESTION. 

Digestion  converts  food  into  forms  which  can  be  dissolved  in 
water,  or  absorbed  and  utilized  by  the  body.  The  digestive 
organs  vary  in  size,  shape,  and  capacity  with  different  kinds  of 
animals.  Some  animals,  such  as  dogs,  fowl,  pigs,  and  men,  have 
short  digestive  organs,  adapted  only  to  concentrated  foods,  such 
as  meat,  cereal  grains,  etc.  The  digestive  organs  of  other 
animals,  such  as  sheep,  goats,  cows,  etc.,  are  large  and  adapted  to 
bulky  food  containing  small  amounts  of  nourishment.  Horses 
and  hogs  have  smaller  digestive  organs. 

Outline  of  Digestive  Process. — The  first  step  in  digestion  is 
preparation  of  the  food  by  chewing  or  grinding.  This  usually 
takes  place  in  the  mouth.  The  food  is  there  moistened  with 
saliva,  a  slightly  alkaline  liquid,  which  not  only  softens  the  food 
and  lightens  the  labor  of  chewing,  but  contains  an  enzyme  termed 
ptyalin  which  converts  starch  into  sugar.  Most  of  the  work  of 
digestion  is  performed  by  enzymes,  substances  which  have  the 
power  of  transforming  other  substances  into  simpler  substances 
without  themselves  being  changed.  Ptyalin  acts  only  in  an 
alkaline  medium,  and  as  soon  as  the  food  becomes  acid  by  fermen- 
tation or  by  means  of  the  gastric  juice,  its  action  stops.  Grinding 
or  other  preparation  of  the  food  before  feeding  will  partly  de- 
crease the  labor  of  chewing.  Grinding  is  especially  necessary 
for  pigs,  or  for  other  animals  when  small  hard  seed  are  fed. 
When  whole  grain  is  fed  to  cattle,  it  is  sometimes  imperfectly 
masticated,  and  a  considerable  number  of  grains  passes  through 
undigested. 

The  sheep  and  the  ox  have  four  stomachs.  The  first  and  sec- 
ond stomachs  are  used  to  store  the  food  until  it  is  returned  to 
the  mouth  for  a  second  mastication.  The  food  then  passes  to  the 
third  stomach,  which  has  a  sieve-like  structure,  where  the  food  is 
kneaded  and  ground  up.  The  digestion  takes  place  in  the  fourth 
stomach. 

These  animals  are  called   ruminants,  and  are  able  to  utilize 


DIGESTION  393 

coarser  feed  than  animals  which  have  only  simple  stomachs. 
Fermentation  takes  place  in  the  first  stomach  of  ruminants,  since 
temperature  and  other  conditions  are  very  favorable  to  the  action 
of  bacteria.  Lactic  acid  is  produced  from  soluble  carbohydrates, 
proteids  are  split  up,  amides  are  affected,  and  even  crude  fiber 
may  undergo  some  slight  change.  Carbon  dioxide,  hydrogen, 
marsh  gas,  acetic  acid,  butyric  acid,  and  lactic  acid  are  some  of 
the  products  of  the  fermentation.  This  process  dissolves  some 
of  the  nutrients,  and  breaks  up  the  cell  walls,  thereby  allowing 
the  entrance  of  digestive  juices.  It  also  softens  the  materials  and 
so  favors  the  disintegration  of  hard  vegetable  structures  when 
chewed  again  in  the  mouth.  The  acids  which  are  formed  grad- 
ually decrease  the  fermentation,  until  they  finally  stop  entirely 
the  action  of  the  bacteria,  since  an  acid  medium  is  unfavorable 
to  their  activity. 

Stomach  Digestion. — When  food  enters  the  true  stomach,  the 
gastric  juice  is  slowly  poured  upon  it.  The  gastric  juice  contains 
hydrochloric  acid,  lactic  acid,  and  three  enzymes,  which  can  act 
only  in  an  acid  medium.  Pepsin  splits  up  the  proteids  into 
albumoses  and  peptones.  Rennin  which  is  found  largely  in  the 
stomach  of  young  animals,  coagulates  the  casein  of  milk  and 
other  proteids.  Lipase  splits  fats  and  oils  into  glycerol  and  fatty 
acids.  Proteids  are  digested  chiefly  in  the  stomach,  though  the 
fats  are  also  split  up  and  digested  to  some  extent.  The  proteids 
are  converted  into  peptones  and  albumoses,  which  are  soluble 
and  can  pass  through  the  membranes  of  the  stomach.  Even 
water-soluble  proteids  are  split  up  during  digestion. 

Intestinal  Digestion. — When  the  food  enters  the  intestines,  it  is 
gradually  mixed  with  bile,  the  pancreatic  juice,  and  intestinal 
juices,  and,  being  alkaline,  they  put  an  end  to  the  action  of 
the  gastric  juice. 

Bile  acts  chiefly  to  form  soaps  with  the  fatty  acids  and  to 
emulsify  the  fats  and  oils.  The  emulsion  consists  of  minute 
drops  of  fat,  suspended  in  the  liquid,  and  both  the  emulsified  fat 
and  the  soaps  can  be  absorbed.  Bile  is  also  able  to  convert  starch 
into  sugar. 
26 


394  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  pancreatic  juice  exerts  a  vigorous  digestive  action  upon 
proteids,  fat,  and  starch.  It  contains  trypsin,  which  acts  on  pro- 
teids;  amylopsin,  which  rapidly  changes  starch  into  sugar;  and 
steapsin,  which  emulsifies  and  splits  fat.  The  proteids  are  con- 
verted into  crystallizable  substances,  such  as  leucin,  tyrosin, 
aspartic  acid,  etc.,  as  well  as  albumoses  and  peptones. 

Intestinal  juices  also  exert  a  digestive  action,  especially  on 
protein  and  starch. 

Bacteria  increase  in  numbers  as  the  food  passes  along  the  intes- 
tines; fermentation  and  putrefaction  gradually  supersede  the 
action  of  the  digestive  juices.  In  herbivorous  animals,  digestion 
is  aided  by  the  enormous  number  of  bacteria  present  in  the  lower 
portions  of  the  intestines.  These  bacteria  act  upon  the  undigested 
food,  split  up  fats,  change  starch,  and  other  carbohydrates  into 
lactic,  butyric,  and  acetic  acids,  and  exert  considerable  digestive 
action  on  crude  fiber.  Three  gases,  carbon  dioxide,  marsh  gas, 
and  hydrogen,  are  formed  in  the  process.  The  crude  fiber  is 
digested  only  by  such  fermentation.  A  quantity  of  substances 
which  would  not  be  acted  upon  by  the  digestive  juices  are  dis- 
solved and  made  useful  to  the  animal. 

Absorption. — The  dissolved  nutrients  are  absorbed  to  some 
extent  by  the  walls  of  the  stomach,  but  most  largely  by  the  intes- 
tinal walls,  and  pass  either  directly  into  the  blood,  or  first  into  the 
chyle  and  then  into  the  blood. 

The  Proteids  are  taken  up  as  albumoses,  peptones,  and,  to  some 
extent,  as  leucin,  tyrosin,  and  other  crystallizable  nitrogenous 
bodies.  But  since  these  substances  do  not  occur  in  the  chyle  or 
in  the  blood,  they  must  have  been  synthesized  into  animal  pro- 
teids in  the  membranes  of  the  digestive  organs.  That  is  to  say, 
the  proteids  of  the  food  are  first  split  up,  then  converted  into 
necessary  animal  proteids.  It  is  quite  possible  that  some  of  the 
products  of  the  digestion  of  the  various  proteids,  are  much  better 
suited  to  the  formation  of  animal  proteids  than  others ;  and  some 
products  may  be  entirely  unsuitable  for  the  purpose  of  the 


DIGESTION  395 

systhesis  and  must  be  oxidized.1  It  is  also  possible  that  the  pro- 
ducts of  digestion  of  certain  proteids  may  be  injurious. 

Fats  are  absorbed  as  fatty  acids,  as  glycerol,  as  soaps, 
and  in  a  finely  divided  form  suspended  in  the  digested 
solution,  as  an  emulsion.  There  is  a  union  of  fatty  acids  and 
glycerol  in  the  absorbing  membrane,  so  that  only  fats  enter  the 
chyle  or  blood. 

Carbohydrates  are  converted  into  simple  sugars  (grape  sugar, 
fructose,  etc.,)  or  by  fermentation,  into  acids,  such  as  lactic  acid, 
butyric  acid,  etc.  These  appear  to  some  extent  in  the  chyle,  but 
more  largely  in  the  blood. 

Various  methods  are  used  in  studying  the  processes  of 
digestion.  The  digestive  juices  have  been  secured  from  animals, 
and  their  action  tested  upon  various  constituents  of  the  food. 
The  process  of  digestion  has  also  been  to  some  extent  observed 
through  openings  made  into  the  digestive  organs  by  accident  or 
intention.  The  contents  of  digestive  organs  have  been  removed 
and  examined. 

Rennet,  prepared  from  the  stomachs  of  calves ;  and  pepsin,  pre- 
pared from  animals  killed  in  the  slaughter  house,  are  commercial 
products,  the  former  being  used  in  coagulating  milk  in  the  manu- 
facture of  cheese,  and  the  latter  for  medicinal  purposes.  None 
of  the  digestive  ferments  so  far  isolated  have  the  power  of 
causing  crude  fiber  to  go  into  solution.  The  intestinal  bacteria, 
however,  when  inoculated  into  a  medium  containing  crude  fiber, 
cause  it  to  be  partly  dissolved,  producing  marsh  gas,  carbon 
dioxide,  organic  acids,  and  soluble  products  which  can  be  absorbed 
and  utilized. 

Excretion. — The  undigested  residues,  mixed  with  gallic  acid, 
mucus,  with  other  animal  products  (metabolic  products),  and  with 
digested  but  unabsorbed  material,  are  finally  ejected. 

The  excrement  is  by  no  means  free  of  digestible  materials.  The 
quantity  of  digestible  matter  is  small,  however,  unless  the  food 
is  imperfectly  masticated,  or  unless  its  premature  evacuation  is 
caused  by  digestive  disturbances. 

1  See  Wisconsin  Research  Bulletin  No.  21. 


396  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  time  required  for  the  passage  of  food  through  the  body 
varies  with  different  kinds  of  animals.  Residues  of  the  food 
begin  to  appear  in  12  hours  with  the  dog,  36  hours  with  the  pig, 
and  three  or  four  days  in  the  excrement  of  the  cow,  sheep,  goat, 
or  horse.  The  residues  are  usually  completely  excreted  in  7  to 
8  days  by  cows,  sheep,  and  similar  animals,  though  bulky  food 
may  continue  to  appear  for  14  days  if  followed  by  easily  digested 
food,  such  as  young  grass,  etc. 

Metabolic  Products. — The  transformation  which  food  under- 
goes within  the  animal  is  termed  metabolism,  and  the  products  of 
the  life  action  are  termed  metabolic  products.  The  metabolic 
products  in  the  excrement  are  residues  of  digestive  juices  and 
other  animal  products.  A  portion  of  the  intestine,  isolated  but 
left  within  the  body,  has  been  found  to  collect  a  certain  amount 
of  waste  material,  which,  under  normal  conditions,  passes  into 
the  excrement.  In  ordinary  digestion  experiments,  the  metabolic 
products  in  the  excrement  may,  for  all  practical  purposes,  be 
regarded  as  a  portion  of  the  undigested  food,  since  they  represent 
so  much  material  lost  from  the  body  in  the  excrement.  In 
other  experiments,  however,  the  metabolic  products  must  be 
taken  into  account.  The  metabolic  products  contain  protein,  or 
fat  and  ash,  but  no  carbohydrates  or  crude  fiber.  In  some 
digestion  experiments  with  food  poor  in  fat,  or  with  materials  very 
poor  in  protein,  more  fat  or  protein  has  been  found  in  the  excre- 
ment than  was  present  in  the  food  eaten.  The  quantity  of 
metabolic  fat  is,  however,  small,  and  of  little  importance. 

The  metabolic  nitrogenous  substances  are  of  more  importance. 
There  are  two  ways  of  estimating  the  quantity  of  metabolic 
nitrogen.  One  method  consists  in  feeding  the  animal  on 
materials  nearly  free  of  nitrogen,  and  estimating  the  nitrogen  in 
the  excrement.  For  example,  Pfeiffer  fed  hogs  on  potato  starch, 
cane  sugar,  olive  oil,  and  salts,  a  ration  almost  free  of  nitrogen, 
and  found  the  excrement  to  contain  4.4  per  cent  protein.  Kell- 
ner  obtained  similar  results  with  sheep  which  were  fed  sawdust, 
sugar,  and  starch. 

The   other  method   does   not   give  us   the   exact   quantity   of 


DIGESTION  397 

metabolic  protein,  but  gives  the  maximum  quantity  that  may  be 
present.  Kuhn1  has  devised  a  method  for  estimating  digestible 
protein,  by  means  of  pepsin  and  hydrochloric  acid.  By  experi- 
ments on  animals  he  has  proved  that  the  indigestible  protein  fed 
(estimated  according  to  this  method)  is  exactly  equal  to  the  in- 
digestible protein  excreted.  That  is  to  say,  the  animal  cannot 
digest  the  protein  found  to  be  indigestible  according  to  Kuhn's 


Fig.  83. — Goats  ready  for  digestion  experiment. 
North  Carolina  Station. 

method.  The  metabolic  products  in  an  excrement,  then,  cannot 
be  greater  than  the  protein  digested  from  it  with  pepsin-hydro- 
chloric acid,  though  they  may  be  less. 

As  a  result  of  20  experiments,  Kuhn  found  from  0.36  to  0.58 
gm.  of  pepsin-soluble  nitrogen  in  excrement  from  oxen,  with  an 
average  of  0.48  gm.  for  each  100  gm.  of  digested  dry  matter. 
1  Landw.  Versuchs-stat.,  1894,  p.  204. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  averages  of  other  workers  are  as  follows:  Pfeiffer  0.52 
gm.,  Jordan  0.44  gm.,  Wolfe  0.47  gm.  It  appears  that,  on  an 
average,  not  more  than  0.45  gm.  of  metabolic  nitrogen  (equal  to 
2.8  gm.  protein)  is  excreted  per  100  grams  of  digested  dry  mat- 
ter. Some  metabolic  mineral  matter  is  also  present  in  the  excre- 
ment. 


Fig.  84. — Stall  used  for  digestion  experiments  with  sheep. 
Wyoming  Station. 


Digestion  Experiments. — The  nutrients  which  disappear  during 
the  passage  of  food  through  the  animal  body  are  said  to  be 
digested.  All  that  disappear  do  not  pass  through  the  membranes 
of  the  digestive  organs,  however,  as  some  of  them  are  converted 
into  marsh  gas  and  carbon  dioxide  by  fermentation  and  escape  as 
gases.  The  object  of  a  digestion  experiment  is  to  determine,  by 
trials  on  animals,  the  actual  amounts  of  the  different  nutrients 
which  are  digested.  In  a  digestion  experiment,  a  known  quantity 
of  food  is  fed,  the  excrement  from  it  collected,  and  both  food 
and  excrement  are  subjected  to  analysis.  The  quantity  of  each 
nutrient  fed  and  digested  is  calculated,  and  the  quantity  of 
nutrient  digested  is  divided  by  the  quantity  fed.  The  dividend, 
expressed  as  percentages,  is  the  coefficient  of  digestibility. 


DIGESTION 


399 


With  men,  the  faeces  from  different  meals  are  not  mixed  in 
the  body,  and  can  easily  be  separated  by  appropriate  means. 
Thus,  at  the  meal  before  beginning  the  experiment,  the  man 
swallows  a  capsule  of  charcoal.  Then  for  two  or  three  days  he 
eats  the  ration  to  be  tested.  At  the  end  of  the  period  he  takes 
another  capsule  of  charcoal.  The  dividing  line  between  excre- 
ments from  the  meal  without  charcoal  and  the  one  with  charcoal, 
is  easily  distinguished,  and  the  excrement  from  the  ration  tested 
can  be  separated  easily. 


Fig.  85.— Sheep  arranged  for  digestion  experiment.     Wyoming  Station. 

With  domestic  animals,  the  food  from  different  meals  is  mixed 
so  thoroughly  in  the  stomach  and  intestines  that  not  only  is  it  im- 
possible to  distinguish  one  meal  from  another,  but  the  residues 
from  a  given  meal  may  appear  in  the  excrement  for  three  or 
four  days.  Such  animals  are  fed  a  uniform  quantity  of  food 
long  enough  to  ensure  the  elimination  of  previous  food  residues, 
and  the  excrement  is  collected  for  a  definite  number  of  days.  It 


4OO  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

is  assumed  that  the  excrement  corresponds  to  the  food  fed  on 
corresponding  days.  This  assumption  is  justified  if  the  period 
of  collection  is  long  enough  to  compensate  for  the  irregularities 
in  elimination  of  the  excrement.  A  period  of  only  three  or  four 
days  is  likely  to  give  incorrect  results.  The  collection  period 
should  not  be  shorter  than  six  days  for  pigs,  eight  days  for  sheep, 
and  ten  days  for  cattle.1 

In  digestion  experiments  with  dry  feeding-stuffs,  a  sufficient 
quantity  of  the  feeding-stuffs  should  be  secured  before  the  ex- 
periment is  begun.  After  ascertaining,  by  trial,  how  much  the 
animal  will  eat,  the  feeding  stuff  should  be  mixed  thoroughly, 
and  the  quantities  to  be  fed  each  day  should  be  weighed  out  care- 
fully before  beginning  the  experiment ;  at  the  same  time,  samples 
should  be  taken  for  analysis. 

The  animal  is  fed  exactly  the  same  ration  for  a  period  of  from 
16  to  1 8  days.  The  first  6  to  8  days  feeding  is  for  the  purpose 
of  eliminating  residues  from  the  previous  ration,  and  is  called  the 
preliminary,  or  preparatory  period.  At  the  end  of  this  period 
the  digestion  period  begins,  in  which  the  excrement  is  collected 
for  analysis.  This  lasts  about  10  days.  The  excrement  may  be 
secured  in  rubber  bags  attached  to  the  animal,  or  by  special  stall 
arrangements  which  prevent  the  solid  excrement  from  being 
scattered  or  mixed  with  urine  or  bedding.  With  small  animals, 
the  excrement  is  collected  every  24  hours,  mixed  thoroughly,  and 
an  aliquot  part  dried  at  a  low  temperature  (60-70°  C.).  With 
horses  and  cattle,  the  aliquot  should  be  taken  every  12  hours,  as 
the  large  masses  remain  warm  and  ferment  rapidly.  After  dry- 
ing, the  samples  are  mixed  and  analyzed.  If  green  feeds,  silage, 
or  similar  materials  are  to  be  tested,  equal  quantities  should  be 
weighed  for  feeding  each  day,  and  a  sample  for  analysis  should 
also  be  taken  every  day  and  dried  at  once.  The  quantity  of 
feed  should  be  adjusted  to  the  appetite  of  the  animal  before  the 
preliminary  feeding  period  begins.  Residues,  even  when  weighed 
and  analyzed,  introduce  disturbances  and  diminish  the  value  of 
the  work. 

1  See  Kellner,  Exp.  Sta.  Record  9,  p.  504. 


DIGESTION 


401 


If  a  concentrated  feeding-stuff  is  to  be  tested,  the  digestibility 
of  hay  is  first  determined,  then  the  concentrate  added,  and  the 
digestibility  of  the  mixture  ascertained.  The  nutrients  digested 
from  the  hay  are  subtracted  from  those  digested  from  the  mix- 
ture, and  the  difference  is  assumed  to  represent  the  material 
digested  from  the  concentrate.  It  is  assumed  that  ingredients  of 
the  mixture  are  digested  to  the  same  extent  as  the  feeds  would 
be  separately,  but  this  is  not  always  the  case,  as  we  shall  see.  To 
guard  against  abnormal  conditions  of  the  digestive  organs,  and 
also  to  secure  a  more  accurate  average,  at  least  two  animals 
should  be  used. 

The  following  is  an  example  of  an  experiment1  on  one  sheep. 
The  preliminary  feeding  was  eight  days,  and  the  digestion  period, 
ten  days.  Three  sheep  were  used,  but  the  figures  are  given  for 
for  only  one. 

DIGESTION  EXPERIMENT  WITH  ONE  SHEEP. 


Protein 

Fat 

Crude 
fiber 

Nitro- 
gen-free 
extract 

Water 

Ash 

Alfalfa  hay  fed,  composi- 

1  6  17 

I  AI 

28  1A 

Mo6 

ft   T/t 

Excrement,  sheep  No.  2, 
composition  per  cent  . 
Fed  4,400  gms.  alfalfa,  con- 
taining' gms  

II.  12 
71  1  O 

3-62 

62  o 

40.82 
I   246  I 

.yu 

27.78 
I    ^"*7  2 

lu.yy 

7.26 

940 

-jcft  O 

Excrement,    1,667    gins, 
containing  gms  

185.4 

60.3 

680.5 

463.1 

— 

«X)°-U 
156.7 

Digested 

T   7 

rfiir  A 

O^O-U 
71  Q 

*•  / 

0UO'U 

AC     A 

1,0/4.  l 

ooz  ^ 

/o-y 

*•§ 

uy.y 

Artificial  Digestion. — By  artificial  digestion  we  mean  labora- 
tory tests  to  ascertain  the  digestibility  of  constituents  of  feeding- 
stuffs.  Only  with  proteids  has  any  measure  of  success  been  at- 
tained in  this  way.  As  before  stated,  the  proteids  not  digested 
by  Kuhn's  method  are  not  digested  in  the  animal.  Kuhn's 
method,  then,  offers  us  a  means  for  ascertaining  the  maximum 
digestibility  of  the  protein  of  feeding-stuff.  The  animal  cannot 
digest  any  more  proteids  than  is  indicated  by  the  method,  though 
1  Bulletin  147,  Texas  Exp.  Sta. 


4O2  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

it  may  digest  less.  In  Kuhn's  method,  2  grams  of  feeding-stuff 
are  treated  with  I  gram  of  pepsin  dissolved  in  500  cc.  of  0.2  per 
cent,  hydrochloric  acid,  maintained  at  the  blood  heat  48  hours, 
and  the  hydrochloric  acid  increased  from  0.2  to  i.oo  per  cent,  by 
additions  of  acid  at  intervals  of  12  hours.  The  residue  is  then 
filtered  oft",  washed,  nitrogen  determined  in  it  and  calculated  to 
protein. 

Influence  of  Different  Conditions  on  Digestion. — The  digestion 
of  food  depends  upon  a  number  of  conditions.  The  kind,  variety, 
and  age  of  the  animal,  composition  of  the  rations,  the  prepara- 
tion of  the  food,  and  other  circumstances,  have  been  studied  by 
proper  arrangement  of  the  experiments. 

Kind  of  Animal. — Differences  in  the  digestive  organs,  digestive 
secretions,  and  habits  of  animals  make  considerable  differences 
in  their  digestive  power.  The  digestive  organs  of  sheep  and 
goats  are  twenty-seven  times  as  long  as  their  bodies ;  of  the  ox, 
twenty  times;  of  pigs,  fourteen  times;  and  of  the  horse,  eleven 
times.  Ruminants  have  greater  ability  to  digest  coarse  fodders 
than  other  animals.  Sheep  digest  less  than  cattle,  particularly  of 
coarse  fodders  which  are  hard  to  digest,  apparently  because  the 
contents  of  the  last  intestinal  tract  of  cattle  is  more  moist  and  the 
process  of  fermentation  continues  longer.  The  more  digestible 
the  material,  the  less  the  difference. 

On  account  of  shorter  intestines  and  simpler  organization  of 
the  stomach,  the  horse  has  a  less  digestive  power  than  ruminants, 
especially  for  coarse  fodders.  The  horse  digests  only  about  half 
as  much  from  straw  as  does  the  ox.  The  difference  is  most 
marked  with  crude  fiber  and  ether  extract;  there  is  little  differ- 
ence in  protein,  especially  in  concentrated  feeds. 

Pigs  have  less  digestive  power  than  horses  or  cattle  for  green 
feeds,  and  by-products  containing  much  crude  fiber.  With  grain 
and  oil  cakes  the  difference  is  less ;  but  there  are  many  by- 
products, such  as  brewers  grains,  which  the  pig  digests  poorly. 

The  following  experiments  were  made  to  compare  animals  of 
different  kinds,  fed  on  the  same  fodder: 


DIGESTION 


403 


PERCENTAGES  DIGESTED. 


Organic 
substance 

Crude 
protein 

Nitrogen- 
free  ex- 
tract 

Crude 
fat 

Crude 
fiber 

Oat  straw     Cattle 

^8 

32 

58 
49 

43 
50 

49 

Sheep 

Difference  

IO 

13 

9 

—7 

14 

Meadow  hay     Cattle  •  •  • 

67 
65 

6l 

57 

70 
69 

61 

57 

64 
61 

Sheep  

2 

4 

i 

4 

3 

Meadow  hay,  poor  quality- 
Sheep  

47 

57 

62 
56 

24 

39 

ii 

—3 

6 

22 

19 

5i 

56 

61 

29 

50 
37 

Difference  

5 

— 

-3 

27 

13 

89 

79 

77 

9i 
94 

85 

61 

62 

70 

Horse  

— 

2 

-3 

24 

8 

Clover,  young  —  Ruminant 
Hogs    

74 
54 

74 
49 

83 
7i 

65 
24 

60 
24 

20 

25 

12 

41 

36 

Corn  (grain)  —  Ruminant  .  . 
HOETS  •  • 

91 

72 

94 

85 

77 
44 

Difference 

I 

~7 

— 

ii 

33 

Other  conditions  regarding  digestion  by  the  animal  which  have 
been  studied  are  as  follows  :x 

1.  Different  breeds  of  the  same  animal  have  the  same  average 
digestive  power. 

2.  Different  individuals  of  the  same  variety  may  have  different 
digestive  power,  due  to  faulty  teeth,  too  rapid  consumption  of 
food,  defective  chewing,  great  nervousness,  abnormal  conditions 
of   the   digestive   organs,   chronic   sickness,    or   defects    of   the 
digestive  organs. 

1  Kellner,  Ernahrung  d.  Landw.  Nutztiere,  p.  45. 


404 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


3.  The  age  of  the  animal  has  no  influence,  unless  the  animal  is 
too  young  for  the  food  given,  or  too  old  to  masticate  it  properly 
on  account  of  defective  teeth. 

4.  Animals  resting  or  at  moderate  work  have  the  same  diges- 
tive power.     Vigorous  work  appears  to  cause  a  slight  decrease. 

5.  Variations   in  light,  temperature,   and  other  external  con- 
ditions, if  great  excitement  is  not  caused  thereby,  have  no  effect. 

Composition  of  Feed. — Different  quantities  of  roughage  fed 
alone  are  digested  to  the  same  extent.  This  is  evident  from  the 
experiments  of  Henneberg  and  Stohmann  with  oxen,  and  E. 
Wolff  with  horses  and  sheep. 


Daily   ration 
weight  of  roughage 

Dry 

substance 

Percentages  digested  by  sheep1 

Protein 

Fat 

Nitrogen- 
free  ex- 
tract 

Crude 
fiber 

08   

61 
62 
62 

72 

75 
74 

26 
31 
32 

71 
68 

7i 

44 
48 

47 

JO    

j    2    

Different  quantities  of  roughage  and  concentrates,  mixed  in 
the  same  proportions,  appear  to  be  digested  slightly  less  with  a 
heavy  ration  than  with  a  moderate  ration. 

The  addition  of  fat  and  oil  does  not  affect  the  digestibility  of 
the  other  nutrients,  provided  not  over  I  pound  per  1,000  pounds 
live  weight  is  fed.2  The  oil  must  also  be  emulsified  or  finely 
divided,  for  liquid  oil  may  occasion  depression  in  digestibility, 
probably  because  it  hinders  the  wetting  of  the  food,  and  thereby 
the  entrance  of  the  digestive  juices. 

According  to  many  experiments,  the  addition  of  digestible 
carbohydrates  or  non-protein  will  cause  a  depression  of  digesti- 
bility if  the  proportion  of  protein  to  carbohydrates  is  thereby 
made  too  wide.  The  following  example  is  from  Kuhn,  in  which 
starch  was  added  to  a  ration  of  meadow  hay  fed  to  oxen. 

1  Landw.  Versuchs-stat.,  1878,  p.  19. 

2  Kellner,  Landw.  Versuchs-stat.,  1900,  p.  114  and  199. 


DIGESTION 


405 


Assuming  the  starch  to  be  completely  digested,  the  results  are  as 
follows  i1 

PERCENTAGE  DIGESTIBILITY. 


Organic 

substance 

Protein 

Fat 

Nitrogen- 
free  ex- 
tract 

Crude 
fiber 

62   r 

2Q  2 

61  8 

67  *\ 

Meadow  hay  with  1,662  kg. 

U^O 

eft  o 

D/-u 

zy.^ 

27  O 

CQ    Q 

62  o 

Meadow  hay  with  2,866  kg. 

4y.u 
41    O 

27  o 

Cf)    O 

61  o 

The  depression  in  digestibility  of  protein  may  be  in  part  due  to 
increased  excretion  of  metabolic  products.  As  we  have  seen, 
2.5-3.1  grams  of  protein  are  excreted  from  every  100  grams  of 
digested  dry  substance,  and  the  additional  quantity  of  protein 
excreted  corresponds  very  nearly  to  the  increase  which  would  be 
caused  by  the  addition  of  starch.  However,  we  do  not  yet  know 
the  cause  of  the  decreased  digestion.  Other  carbohydrates,  as, 
cane  sugar,  pectin,  and  purified  cellulose,  have  the  same  effect  as 
starch  in  decreasing  digestibility. 

An  increase  of  protein  can  partly  or  completely  eliminate  the 
depression  caused  by  addition  of  carbohydrates.  For  example, 
Haubner  found  that  the  starch  appeared  in  the  excrement  of 
sheep  fed  on  potatoes,  but  when  rape  cake  was  added  to  the  ration, 
starch  was  no  longer  excreted.  Many  exact  digestion  experi- 
ments have  proved  that  the  addition  of  protein  can  increase  the 
digestibility  of  a  ration  poor  in  protein. 

Non-albuminoid  nitrogenous  compounds,  such  as  asparagin, 
exert  a  similar  effect.  For  example,  Weiske  found  a  ration 
nearly  free  of  nitrogen  digested  86  per  cent.,  with  addition  of 
asparagin  or  fibrin  it  was  digested  92  per  cent.  Kellner  observed 
a  similar  action  when  asparagin  or  ammonium  acetate  was  used. 

Concentrated  feeding-stuffs  exert  an  influence  on  digestion 
according  to  their  content  of  digestible  protein  or  carbohydrates. 
Foods  poor  in  protein,  as  beets  and  potatoes,  exert  a  depressing 
1  Landw.  Versuchs-stat.,  1894,  p.  470. 


406  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

effect  on  digestibility,  unless  fed  in  connection  with  concentrates 
rich  in  protein.  Concentrates  of  intermediate  composition  exert 
an  appreciable  effect  upon  digestion  only  when  the  ration  con- 
tains more  than  8  parts  non-protein  to  I  part  protein.  In  gen- 
eral, it  may  be  stated,  that  the  digestion  of  a  food  is  most  com- 
plete when,  for  7  to  8  parts  digestible  nitrogen-free  nutriment 
(including  fat  X  2-25)>  not  less  than  I  part  digestible  crude  pro- 
tein is  present.  With  pigs,  which  have  a  high  digestive  power  for 
carbohydrates,  the  ratio  may  be  as  wide  as  i :  12. 

Free  acid,  in  moderate  limits,  has  no  influence  upon  digestibility. 
Experiments  were  made  with  sulphuric  acid  and  lactic  acid 
added  to  the  ration  of  sheep  and  oxen,  as  much  as  2.67  per  cent, 
lactic  acid  being  fed.  Free  acids  are  found  in  silage.  Horses 
and  young  animals  are  often  very  sensitive  to  acid.  The  effect 
on  the  teeth  must  also  be  considered. 

Carbonate  of  lime,  even  in  high  amounts,  had  no  effect  upon 
digestibility  by  sheep.  Since  the  acid  gastric  juice  could  not  have 
acted,  being  neutralized  by  the  carbonate  of  lime,  the  work  of 
digestion  must  have  been  performed  by  the  alkaline  pancreatic 
juice. 

Character  of  Feed. — Dry  fodder  has  the  same  digestibility  as 
green  fodder,  when  there  is  no  loss  in  drying,  but  usually  fer- 
mentation takes  place,  or  leaves,  etc.,  are  broken  off,  leaving 
material  of  less  digestible  character.  Young  plants  are,  in  gen- 
eral, more  digestible  than  older  ones,  and  also  have  a  higher  pro- 
ductive value.  Corn,  however,  contains  more  digestible  matter 
when  fully  ripe  than  if  cut  before  the  ears  are  grown.  This  is 
due  to  the  production  of  a  large  quantity  of  highly  digestible 
grain. 

Stage  of  Growth. — The  digestibility  decreases  with  the  stage  of 
growth  of  the  plant,  more  rapidly  as  the  plant  approaches 
maturity.  An  exception  is  Indian  corn,  which  forms  a  large 
amount  of  easily  digested  grain  as  it  approaches  maturity. 

B.  E.  Wolff  obtained  the  following  results  with  clover  cut  at 
different  stages  of  growth: 


DIGESTION 


407 


PERCENTAGES  DIGESTED. 


Nitrogen-free 
extract 

Digested 
nitrogen-free 
extract  and 
fiber 

Green  clover  — 

A1   ^ 

4o-o 
A-t  7 

D*07 

A7  Q 

4o-y 

A7    ^ 

A1   8 

4/  O 

4o-° 

Preparation  of  Food. — Cooking,  steaming,  roasting,  etc.,  de- 
crease the  digestibility  of  the  protein  of  the  food.  Grinding  is 
better  for  hard  seeds,  or  for  those  which  are  so  small  as  to  be 
liable  to  escape  mastication,  such  as  flax,  barley,  sorghum,  millet, 
etc.  Horses  and  hogs  masticate  food  less  thoroughly  than 
ruminants,  and  hence  derive  more  benefit  from  grinding. 

The  following  are  some  American  experiments1  relating  to 
these  conditions : 

COEFFICIENTS  OF  DIGESTIBILITY. 


Protein 

Crude 
fiber 

Nitrogen- 
free  ex- 
tract 

Ether 
extract 

67.8 
46.9 

75-5 
65.9 

49-6 

51.4 

87.I 
71.7 

Decrease  due  to  roasting  

20.9 

9.6 

-1.8 

5-4 

Oat  fodder   early  cut  (sheep)   ..... 

72.3 
67.8 

54-6 

43-5 

6>5 
61.1 

70.2 
67.5 

Oat  fodder  late  cut  (sheep)  

4-5 

u.  i 

2.4 

2.7 

Timothy   full  bloom  (sheep)  

60.4 
44-5 

62.1 

51-7 

71.8 
61.0 

51-5 
34-6 

15-9 

10.4 

10.8 

16.9 

86.1 
68.7 

29.4 
38.3 

94-2 
88.8 

81.7 
45-6 

174 

-8.9 

5-4 

36.1 

1  Bulletin  No.  77,  Office  Exp.  Sta. 


408 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Coefficients  of  Digestibility. — The  following  are  coefficients  of 
digestibility  of  a  few  feeding-stuffs.1 

COEFFICIENTS  OF  DIGESTIBILITY  OF  SOME  FEEDING  STUFFS. 


Protein 

Ether 
extract 

Crude 
fiber 

Nitrogen- 
free  ex- 
tract 

QQ  A 

6n  6 

Cottonseed  nulls 

93-3 

(«c   n 

55-5 

\Vheat  bran    

J^.U 

77  8 

°vV/ 

68  o 

96  6 

41.  1 
60  A 

Wheat  shorts  

//.o 
7Q  8 

86  i 

°9-4 

8  1     7 

Corn  tneal  

67  Q 

00.3 

33-  J 

Corn  cobs  

w-y 

IQ   7 

yz.i 

CQ     T 

y4-° 

Xl8    7 

17-O 
60   I 

0^.  A 
QT    T 

o/O 

09.1 

yi.i 

V^'O 

A£I  A 

68  /i 

/O-6 

4U*O 

40.4 

O/'O 

3-3 
78  6 

•9 
60  i 

5r-5 
6n  6 

i*»O 

«5°'0 
/i/t  6 

°9-o 
66  9 

cA  Q 

Rice  straw  

4O-V 

26  6 

c8  o 

ou<4 

4/-  J 

Digestibility  of  Constituents  of  Nitrogen-Free  Extract.-' — Inves- 
tigations as  to  the  digestibility  of  the  constituents  of  nitrogen- 
free  extract,  show  that  the  sugars  and  the  true  starch  are  prac- 
tically completely  digested  when  the  food  is  properly  masticated. 
The  pentosans  are  digested  to  about  the  same  extent  as  the  nitro- 
gen-free extract,  while  the  remaining  and  unknown  constituents 
of  the  nitrogen-free  extract  have  a  much  lower  digestibility.3  It 

COEFFICIENTS  OF  DIGESTION  OF  CRUDE  FIBER  AND  OF  CONSTITUENTS 
OF  THE  NITROGEN-FREE  EXTRACT. 


Feed 

Crude 
fiber 

Nitrogen-free  extract 

Sugars 

Starch 

Pentosans 

Residue 

54-6 
52.3 
67-3 

86.2 

IOO.O 

95.0 

IOO.O 
IOO.O 

97-4 

99.6 
25.0 

86.5 
58.0 
6r.o 

65.2 
50.0* 
32-74 

Cottonseed  meal  and  hulls. 
Timothy  hay  .... 

Qi-aJ3orra.ss  hay  

1  Bulletins  147,  104,  Texas  Exp.  Sta.;  Bulletin  77,  Office  Exp.  Sta. 
-  Headden,  Bulletin  124,  Colorado  Station. 

3  Fraps,  Bulletin  104,  Texas  Exp.  Sta. 

4  Starch  included. 


DIGESTION 


409 


is  possible  that  the  fermentation  and  other  changes  which  food 
undergoes  within  the  animal,  modify  the  crude  fiber  so  that  a 
portion  of  it  becomes  soluble  in  acids  or  alkali,  and  thus  appears 
as  a  portion  of  the  nitrogen-free  extract. 

Digestibility  of  Ether  Extract  Constituents. — The  ether  extract 
of  concentrates  consists  chiefly  of  fats  and  oils,  but  that  of  rough- 
ages contain  on  an  average  nearly  60  per  cent,  unsaponifiable  mat- 
ter, chiefly  wax  alcohols,  as  previously  pointed  out.  It  has  been 
long  observed  that  the  ether  extracts  of  hays  and  fodders  have 
a  low  digestibility.  Indeed,  in  a  number  of  experiments,  more 
ether  extract  was  found  in  the  excrement  than  was  present  in  the 
hay. 

A  study  of  the  digestibility  of  the  constituents  of  the  ether 
extract  shows  that  while  the  unsaponifiable  materials  or  wax 
alcohols  have  a  low  coefficient  of  digestibility,  the  saponifiable 
material,  containing  the  fatty  acids  and  chlorophyll,  have  a  much 
higher  digestibility.  Thus  the  observed  low  digestibility  of  the 
ether  extract  of  hays  and  fodders  is  due  to  the  small  content  of 
fats  and  oils  and  the  high  content  of  waxes  and  alcohols  less 
easily  digested. 

PERCENTAGE  DIGESTIBILITY  OF  CONSTITUENTS  OF  ETHER  EXTRACT^ 


Total 
extract 

Unsaponi- 
fiable 

Saponi- 
fiable 

Alfalfa  hay  

Bermuda  hay  .... 

•y 

59-1 

Burr  clover  .... 

6L  * 

Q  f. 

"8  6 

28  O 

6/1    A 

Johnson  grass  hay  

cj   2 

04.4 
60   I 

;>•*•* 

AC    O 

12   8 

Millet 

rf.   A 

,>»•  * 

//•4 
o,    A 

OD>4 

T5-9 

01.4 

Composition  and  Heat  Value  of  Digested  Nutrients. — We  may 
determine  the  composition  of  digested  crude  fiber  by  the  follow- 
ing method :     The  crude  fiber  fed  in  the  feed  and  the  crude  fiber 
excreted  in  the  digestion  experiment  are  subjected  to  analysis. 
The  quantity  of  carbon,  hydrogen,  and  oxygen  fed  in  the  crude 
1  Fraps  and  Rather,  Bulletin  150,  Texas  Station. 
27 


4io 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


fiber  and  the  quantity  excreted,  is  calculated  from  the  known 
amounts  of  crude  fiber  fed  and  excreted.  The  quantity  of  crude 
fiber  digested,  and  the  quantity  of  carbon,  hydrogen,  and  oxygen 
digested,  are  calculated  from  the  data.  From  these  figures  we 
can  calculate  the  composition  of  the  digested  crude  fiber. 

The  crude  fiber  and  the  nitrogen-free  extract  in  the  excrement 
contain  more  carbon  and  hydrogen  than  that  digested,  and  have 
a  higher  heat  value.  Digested  crude  fiber  and  digested  nitrogen- 
free  extract  have  been  found  to  have  the  composition  and  heat 
value  of  a  carbohydrate.  For  this  reason,  the  digested  crude 
fiber  and  nitrogen-free  extract  are  often  referred  to  as  carbo- 
hydrates. The  lignin  is  not  digested. 

The  composition  of  digested  ether  extract,  protein,  etc.,  can 
be  determined  in  the  same  way.  The  heat  value  of  the  digested 
nutrients  is  estimated  by  a  procedure  somewhat  similar. 

Ether  extract  of  hays,  grasses,  and  other  coarse  feeding-stuffs 
contain  waxes,  etc.,  as  we  have  seen,  which  are  not  digested  so 
well  as  fats.  They  accumulate  in  the  excrement  and  change  its 
composition.  The  composition  and  heat  value  of  the  digested 
ether  extract  is  about  the  same  as  pure  fat,  while  the  ether  ex- 
tract in  the  excrement  has  a  much  higher  heat  value. 

Proteids  have  a  heat  value  of  5,479  to  5,990  cal.  per  gram.  The 
digested  proteids  have  practically  the  same  value.  The  average 
is  5,711  calories. 

HEAT  VALUE  OF  CONSTITUENTS  OF  MEADOW  HAY. 


Crude 
fiber 

Nitrogen- 
free  ex- 
tract 

Ether 
extract 

Heat  value  of  I 

4,426 
4,782 
4,220 

4,584 
5,265 
4,232 

9,194 
9,821 
8,322 

in  Excrement  

F)i  crperprl 

CHAPTER  XX. 


UTILIZATION  OF  FOOD. 

Food  is  used  by  animals  to  maintain  the  body  activities  and 
restore  waste  of  material.  It  is  also  used  for  the  production  of 
new  material  in  growth  and  fattening,  for  milk  production,  and 
for  energy  to  produce  work.  Whenever  energy  or  heat  are  to  be 
generated,  oxygen  unites  with  the  substances,  forming  carbon 
dioxide  and  water  from  fats,  organic  acids,  sugars,  etc.,  and 
carbon  dioxide,  water,  and  urea  or  other  nitrogenous  waste  pro- 
ducts, from  proteids.  The  carbon  dioxide  is  eliminated  by  the 
lungs,  and  the  nitrogenous  waste  passes  off  in  the  urine.  The 
oxidation  does  not  take  place  at  one  time,  but  a  number  of  inter- 
mediate products  are  formed. 

The  following  is  the  average  composition  of  ten  kinds  of 
animals,  according  to  analyses  made  by  Lawes  and  Gilbert,  at 
Rothamsted : 

Per  cent. 

Protein    13.5 

Fat 28.2 

Water 49.0 

Ash 3.2 

Contents  of  stomach  and  intestines 6.  i 

Total    IGO.O 

The  ash  consists  of  approximately  86  per  cent,  calcium  phos- 
phate, and  12  per  cent,  calcium  carbonate,  with  small  quantities 
of  fluorides,  chlorides,  iron,  potash,  and  magnesia.  These 
materials  must  all  be  supplied  by  the  food. 

Different  nutrients  of  food  have  different  values  for  the  pur- 
poses above  stated.  The  first  bodily  activity  with  respect  to  food 
is  its  mastication  and  digestion.  This  consumes  food  material, 
which  although  derived  from  food  previously  eaten,  must  be  re- 
placed by  the  food  being  eaten.  Different  kinds  of  food  require 
different  amounts  of  energy  in  mastication  and  digestion.1 

The  food  material  remaining  after  deducting  the  losses  due  to 
mastication,  digestion,  and  undigested  residues,  may  be  used  for 
1  Hagemann,  Exp.  Sta.  Record  10,  p.  906. 


412  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

the  purposes  of  the  body.  The  necessary  vital  functions  must 
first  be  subserved,  such  as  the  body  heat,  beating  of  the  heart, 
movements  of  the  lungs,  etc.,  and  all  other  functions  necessary 
for  the  maintenance  of  the  life  of  the  animal. 

Any  food  values  remaining  after  maintaining  the  animal,  may 
be  used  for  productive  purposes,  such  as  work,  building  of  fat  or 
flesh,  production  of  milk,  etc. 

The  utilization  of  the  various  foods  and  nutrients  by  the  body 
is  studied  by  means  of  exact  experiments  on  animals.  The 
experiment  must,  of  course,  be  adapted  to  the  end  in 
view.  A  study  of  the  income  and  outgo  of  nitrogen  is 
called  the  nitrogen  balance.  A  loss  of  nitrogen  means  a 
loss  of  flesh ;  a  gain  of  nitrogen,  a  gain  of  flesh.  The 
income  and  outgo  of  carbon,  taken  in  connection  with  the  nitro- 
gen balance,  gives  the  loss  or  gain  of  fat.  This  is  called  the  car- 
bon balance.  The  determination  of  the  income  and  outgo  of 
energy  is  called  the  energy  balance. 

The  Nitrogen  Balance. — In  order  to  determine  the  exact  amount 
of  nitrogen  the  animal  is  gaining  or  losing,  we  proceed  as  in  a 
digestion  experiment,  but  collect  and  analyze  the  urine  in  addition 
to  the  solid  excrement. 

The  total  quantity  of  nitrogen  in  the  food  fed  is  the  income  of 
nitrogen.  The  nitrogen  in  the  solid  excrement  is  undigested 
material;  that  in  the  urine,  is  the  digested  nitrogen  which  has 
undergone  complete  metabolism  in  the  body.  The  nitrogen  in 
the  perspiration  is  so  small  that  it  is  usually  not  considered. 

Income  in  food  less  outgo  in  solid  and  liquid  excrement  is  the 
loss  or  gain  of  nitrogen.  If  income  is  greater  than  the  outgo 
there  is  a  gain ;  if  less,  a  loss  of  nitrogen.  Since  over  ninety  per 
cent,  of  the  nitrogen  in  the  animal  body  is  in  the  form  of  flesh,  a 
loss  or  gain  of  nitrogen  represents  a  loss  or  gain  of  flesh. 

Water  and  fat-free  flesh  has  been  found  to  contain,  on  an 
average,  16.67  Per  cent-  of  nitrogen  and  52.54  per  cent,  of  carbon. 
That  is,  i  gram  of  nitrogen  is  contained  in  6  grams  of  dry  flesh, 
which  also  contains  3.15  grams  carbon.  Flesh  contains  on  an 
average  77  per  cent,  water.  Hence  a  gain  of  i  gram  of  nitrogen 


UTILIZATION   OF   FOOD 


413 


means  a  gain  of  3.17  grams  of  carbon  in  dry  flesh,  and  a  gain  of 
26  grams  of  moist  flesh  or  muscular  tissue. 

The  Carbon  Balance. — Carbon  enters  the  animal  in  food  and 
water,  and  leaves  it  in  urine,  solid  excrement,  perspiration,  and 
as  the  gaseous  bodies-carbon  dioxide  and  marsh  gas.  The  marsh 
gas  and  part  of  the  carbon  dioxide  comes  from  the  fermentation 
in  the  intestines,  but  most  of  the  carbon  dioxide  comes  from 
oxidation  of  carbonaceous  bodies  in  the  animal.  For  example, 
the  air  inhaled  and  expired  by  a  horse  was  found  to  have 
approximately  the  following  percentage  composition : 


Inhaled 

Exhaled 

Ox 

20  96 

16  oo 

o  o^ 

A   AO 

The  following  table  gives  an  example  of  the  determination  of 
the  carbon  and  the  nitrogen  balance : 

CARBON  AND  NITROGEN  BALANCE.1 


Nitrogen 

Carbon 

Income  per  day  : 

grams 

69.96 

50.9 
27.50 

37-05 
2.OI 

grams 

2,010.8 
1,572.0 
408.8 
138.4 
1,443.0 
2-7 

177.47 

5,575.5 

Outgo  per  day  : 

106.55 
73.69 

1,609.6 

170.9 
3,112.5 

180.24 
7.23 

4,892.0 

672.5 

The  gain  of  7.23  grams  of  nitrogen  means  a  gain  of  7.23  times 
6  equals  43.4  grams  of  dry  flesh,  containing  22.8  grams  of  carbon. 
1  Kellner,  Landw.  Versuchs-stat.,  1900,  p.  4. 


414  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

This  quantity  of  carbon,  subtracted  from  672.5  grams,  leaves 
649.7  grams  carbon,  which  is  contained  in  849.3  grams  of  fat, 
since  beef  fat  contains  76.5  per  cent,  carbon.  Hence  this  animal 
gained  43.4  grams  of  flesh  and  849.3  grams  of  fat  per  day : 

Apparatus  to  Determine  the  Carbon  Balance. — The  respiration 
apparatus1  consists  essentially  of  an  air-tight  chamber  to  hold  the 
animal,  provided  with  a  window  and  door  and  suitable  openings 
for  the  introduction  of  food  and  water.  A  current  of  air  is 
sucked  through  the  apparatus  by  a  ventilating  fan  connected  with 
a  gas  meter  for  measuring  the  volume  of  the  air  drawn  through. 
A  portion  of  the  air  entering  the  chamber  is  sucked  out  by  a 
mercury  pump  and  measured  by  a  sma1!  gas  meter.  It  then 
passes  through  a  series  of  tubes  containing  a  solution  of  barium 
hydroxide,  of  known  strength,  to  absorb  the  carbon  dioxide. 
Barium  carbonate  is  precipitated,  and  the  excess  of  barium 
hydroxide  can  be  determined  by  titration  with  an  acid  of  known 
strength.  The  carbon  dioxide  may  also  be  absorbed  by  soda  lime 
and  weighed.  This  gives  the  amount  of  carbon  dioxide  in  the 
air  subjected  to  analysis,  and  the  total  quantity  contained  in  the 
known  quantity  of  air  which  passes  through  the  respiration 
chamber  can  be  easily  calculated.  Another  measured  portion  of 
the  air  passes  through  a  tube  containing  copper  oxide,  heated  red 
hot  by  means  of  a  combustion  furnace,  and  then  through  a  sec- 
ond series  of  barium  hydroxide  tubes.  The  marsh  gas  or  other 
organic  carbon  compounds  are  oxidized  in  the  tube  to  carbon 
dioxide,  which  is  absorbed  by  the  barium  hydroxide  as  before. 
We  thus  know  the  total  quantity  of  carbon  as  carbon  dioxide  and 
as  organic  carbon,  which  goes  into  the  respiration  chamber  with 
the  air  taken  in. 

Measured  portions  of  the  air  which  goes  out  of  the  chamber 
are  withdrawn,  and  passed  through  an  apparatus  exactly  similar 
to  that  described  above.  The  exact  quantity  of  carbon  in  carbon 
dioxide  and  in  organic  forms  given  off  by  the  animal,  is  the 
difference  between  that  in  the  air  which  leaves  and  that  which 
enters  the  respiration  chamber. 
1  Exp.  Station  Record  10,  p.  813. 


UTILIZATION  OF  FOOD  415 

Energy  Balance. — The  energy  balance  may  be  determined  in 
two  ways: 

First,  the  energy  in  the  food  fed,  and  in  the  solid  and  the  liquid 
excrement  may  be  determined  by  direct  measurements,  and  that 
lost  as  marsh  gas  calculated.  The  heat  value  of  the  fat  or  flesh 
gained  or  lost  may  be  calculated  from  the  loss  or  gain  of  fat  and 
flesh  found  by  the  nitrogen  and  the  carbon  balance.  From  these 
figures  we  estimate  indirectly  the  energy  used  by  the  animal  body. 

Second,  the  determination  of  energy  in  the  food  and  in  solid, 
liquid,  and  gaseous  excrements  is  made  as  stated  above,  but  the 
energy  given  off  by  the  animal  is  measured  directly.  This  form 
of  experiment  requires  the  use  of  a  respiration  calorimeter.1  The 
results  of  the  two  methods  should,  of  course,  agree,  but  the  sec- 
ond method  is  adapted  to  studying  problems  which  cannot  be 
solved  by  the  first.  For  example,  the  energy  given  off  during  the 
time  digestion  is  going  on  may  be  compared  with  that  given  off 
when  no  digestion  is  going  on.  In  experiments  with  human  be- 
ings, the  extra  energy  given  off  during  reading,  work,  etc.,  may 
be  determined.2 

Respiration  Calorimeter. — A  respiration  calorimeter  consists  of 
a  respiration  chamber  arranged  so  that  the  heat  given  off  by  the 
animal  can  be  measured.  The  chamber  is  insulated  so  that  as 
little  heat  as  possible  may  be  lost  or  gained  by  it.  The  incoming 
air  is  cooled  to  a  uniform  temperature,  and  the  outgoing  air  is 
cooled  to  the  same  extent.  The  heat  given  off  by  the  animal  is 
taken  up  by  water  circulating  through  tubes  inside  the  chamber. 
The  temperature  of  the  water  is  taken  before  it  enters  the  cham- 
ber, and  when  it  leaves.  The  volume  of  water  and  the  difference 
in  temperature  of  the  incoming  and  outgoing  water  being  known, 
the  heat  eliminated  is  easily  calculated  to  calories..  Allowance 
is  also  made  for  the  heat  changes  involved  in  the  condensation 
of  water  on  the  sides  of  the  chamber,  and  for  evaporation  during 
the  experiment. 

1  Armsby,  Bulletin  104,  Pennsylvania  Station.     Exp.    Sta.    Record  15, 
P-  1033- 

2  For  description  of  human  calorimeter  see  Bulletin  63,  Off.  Exp.  Station. 


416 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


A  respiration  calorimeter  is  a  complicated  and  expensive  ap- 
paratus, but  it  secures  information  regarding  the  use  of  nutrients 
and  the  nutrition  of  the  animal  which  is  of  the  highest  value,  and 
which  can  be  secured  in  no  other  way. 


Fig.  86. — Model  of  respiration  calorimeter  at  the  Pennsylvania 
Station.     U.  S.  D.  A. 


Disposition  of  Food  Materials. — The  carbon   which   enters  an 
animal  in  food,  is  disposed  of  as  follows : 

1 i )  A  portion  appears   as   undigested   material   in    the   solid 
excrement. 

(2)  A  portion  escapes  as  marsh  gas  and  carbon  dioxide,  pro- 
duced by  fermentation. 

(3)  A  portion  is  eliminated  as  partly  oxidized  compounds  in 
the  urine. 

(4)  A  portion   is  eliminated  as  carbon  dioxide  in  the  gases 
expired  from  the  lungs,  being  fully  oxidized  in  the  body. 

(5)  A  portion  is  used  in  the  production  of  hair,  flesh,   fat, 
milk,  etc. 


UTILIZATION  OF  FOOD 


417 


The  nitrogen  appears  as  follows : 

(1)  In  the  undigested  residues. 

(2)  In  the  urine. 

(3)  In  perspiration  (very  small  quantity). 

(4)  Used  in  the  production  of  hair,  flesh,  milk,  etc. 
The  energy  is  used  as  follows : 

1 i )  A  part  appears  in  the  undigested  solid  excrement. 

(2)  A  part  is  used  in  fermentation  and  escapes  as  heat. 

(3)  A  part  is  lost  in  incompletely  oxidized  organic  matter  in 
the  urine. 

(4)  A  part  escapes  in  marsh  gas  produced  by  fermentation  in 
the  intestines. 


Fig.  87.— Curve  showing  heat  production  of  steers  in  respiration  calorimeter, 

the  arrows  being  pointed  up  if  the  animal  is  standing. 

Pennsylvania  Station. 

(5)  A  portion  is  used  to  masticate  and  digest  the  food,  and  is 
eliminated  as  heat. 

(6)  A  portion  used  for  bodily  activities,  such  as  beating  of 
the  heart,  breathing,  movements,   warming  the  body,   etc.,   and 
is  eliminated  as  heat. 

(7)  Any  portion  remaining  after  the  above  requirements  are 
satisfied,  may  be  used  for  external  work,  stored  up  in  fat  or 
flesh,  or  used  in  the  production  of  milk,  etc. 

Production  of  Marsh  Gas. — The  effect  of  different  nutrients  or 
foods  upon  the  production  of  marsh  gas  has  been  studied  by  the 
following  method.  First,  the  quantity  of  marsh  gas  evolved  with 


4i8 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


a  given  ration  is  exactly  determined  in  the  respiration  chamber. 
Then  the  marsh  gas  evolved  with  the  same  ration  plus  fat,  pro- 
tein, starch,  crude  fiber,  or  any  other  nutrient  or  feed,  is 
determined.  The  increase  or  decrease  in  the  quantity  of  marsh 
gas  evolved,  shows  the  effect  of  the  addition. 

In  this  way  it  was  found  that  fat  and  proteids  do  not  affect 
the  quantity  of  marsh  gas.  The  methane  appears  to  come  en- 
tirely from  the  constituents  of  the  nitrogen-free  extract  and 
crude  fiber.  The  ratio  of  protein  to  non-protein,  and  other 
factors,  also  appears  to  affect  its  production.  All  additions  which 
decrease  the  digestibility  of  the  nitrogen-free  extract  decrease 
the  production  of  methane,  but  in  greater  proportion;  and  addi- 
tions which  increase  the  digestibility  of  the  nitrogen-free  extract 
increase  the  production  of  methane.  The  various  factors  which 
affect  the  production  of  methane  require  further  study. 

A  considerable  portion  of  the  value  of  the  digested  nitrogen- 
free  extract  and  crude  fiber  is  lost  as  marsh  gas,  as  is  seen  from 
the  following  table : 


Sugar 

Starch 

Crude  fiber 
(paper  starch) 

Nitrogen-free 
extract  and 
crude  fiber 
(average  of  100 
experiments) 

Grams  methane  for  100 

2  8/1 

317 

4A6 

420 

Heat  value  of  methane- 
Heat  value  of  substance 

37-9  Cal. 
395-5  Cal. 
o  6 

42.3  Cal. 
418.3  Cal. 

58.6  Cal. 
418.5  Cal. 

•*y 

57-2  Cal. 
418.4  Cal. 

y.o 

I3-7 

A  considerable  percentage  of  the  material  which  does  not 
appear  in  the  solid  excrement  during  a  digestion  experiment  is 
not  really  digested,  i.  e.,  converted  into  soluble  products  and 
absorbed  by  the  body,  but  is  fermented  and  a  portion  of  its 
value  is  lost  as  marsh  gas. 

Organic  Matter  of  the  Urine. — The  digested  nitrogenous  bodies 
which  have  been  oxidized  by  the  animal  body  are  excreted  in  the 
urine,  in  the  form  of  urea  CO(NH2)2,  uric  acid  C5H4N4O3, 
creatin  C4H9N3O2,  or  hippuric  acid,  C6H5CO.NHCH2COOH, 


UTILIZATION  OF  FOOD  419 

and  possibly  other  compounds.  All  these  substances  are  incom- 
pletely oxidized,  and  represent  a  loss  of  energy  from  the  food. 
Non-nitrogenous  organic  substances  are  also  present  in  the  urine. 
For  example,  the  following  is  an  analysis  of  the  urine  of  a 
sheep : 

Water 86.48 

Urea 2.21 

Hippuric  acid 3.24 

Ammonia 0.02 

Carbonic  acid 0.42 

Other  organic  substances 2.07 

Ash 5.56 


The  effect  of  various  substances  upon  the  urine  may  be  studied 
by  determining  the  amount  and  composition  of  the  urine  with  a 
given  ration,  adding  the  substance  to  be  studied  to  the  ration,  and 
determining  the  change  in  the  urine  caused  by  the  addition.  This 
effect  is  usually  expressed  in  terms  of  energy  (calories).  Kell- 
ner,1  assuming  that  only  the  proteids  fed  affected  the  loss  of 
energy  in  the  urine,  obtained  the  following  results  with  certain 
concentrates : 

Average  energy  in  i  gram  digested  proteids,  Calories  •  ••     5.71 

Average  loss  of  energy  in  urine  from  i  gram,  Calories 1.29 

Average  percentage  loss  of  energy  in  urine 22.6 

Maximum  percentage  loss  (with  linseed  meal) 26.6 

Minimum  percentage  loss  (with  gluten  meal) 18.9 

The  assumption  of  Kellner,  however,  is  not  correct,  since  the 
other  constituents  of  the  food  have  some  effect  upon  the  loss  of 
energy  in  the  urine.  Only  traces  of  sugar  or  pentosans  are  found 
in  normal  urine,  but  an  addition  of  roughage  to  a  ration  increases 
the  loss  of  energy  in  the  urine  to  a  considerably  greater  extent 
than  the  addition  of  an  equal  quantity  of  protein  in  the  con- 
centrated feeding-stuffs  mentioned  above.  Sometimes  the  in- 
creased loss  is  greater  than  the  quantity  of  energy  in  the  proteids 
fed  in  the  roughage.  Non-nitrogenous  substances,  therefore, 
1  Die  Ernahrung  d.  Landw.  Niitzture,  p.  83. 


420  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

suffer  a  loss  of  energy  in  the  urine,  but  at  present  little  is  known 
as  to  the  nature  of  this  loss  and  what  factors  modify  it. 

Available  Energy. — A  portion  of  the  energy  in  the  food  fed  to 
the  animal  remains  in  the  undigested  matter  of  the  solid  excre- 
ment, a  portion  appears  in  the  urine,  and  a  portion  is  lost  in  the 
form  of  marsh  gas.  None  of  the  energy  so  lost  is  of  any  value 
to  the  animal,  and  may  be  termed  unavailable  energy.  The 
available  energy  is  the  total  energy  in  the  nutrients  less  the  losses 
in  the  solid,  liquid,  and  gaseous  excrements.  A  portion  of  the 
available  energy  is  expended  in  the  processes  of  mastication, 
moving  the  food,  preparation  of  digestive  juices,  digestion,  and 
other  operations  necessary  to  bring  the  digested  nutrients  into 
the  body,  and  convert  them  into  forms  suitable  for  its  use.  This 
energy  does  not,  of  course,  come  from  the  food  actually  in  pro- 
cess of  digestion,  but  the  digested  food  must  replace  the  energy 
so  used.  The  energy  used  in  digestion,  etc.,  appears  as  heat,  and 
may  aid  to  keep  the  animal  warm,  but  any  excess  over  the  amount 
so  required,  serving  no  useful  purpose,  is  evolved  as  heat.  We 
will  term  the  energy  consumed  in  digestion  of  the  food  thermal 
energy. 

The  available  energy  remaining  after  the  thermal  energy  has 
been  subtracted,  may  be  used  for  processes  requisite  to  the  life 
of  the  animal,  such  as  to  keep  the  animal  warm,  to  furnish  energy 
for  beating  of  the  heart,  breathing,  and  necessary  movements  of 
the  body.  Any  excess  over  that  needed  by  the  animal  body  may 
be  used  for  productive  purposes — for  fat,  flesh,  milk,  etc.  We 
will  term  this  portion  of  the  energy  of  the  food  its  kinetic  energy. 

Estimation  of  the  Energy  Expended  in  Digestion. — Two  meth- 
ods may  be  used  to  estimate  the  energy  expended  in  digestion  of 
food.  The  first  method  can  be  applied  only  to  animals,  such  as 
the  dog,  having  small  digestive  organs,  which  can  be  completely 
emptied  by  starving  for  a  few  days.  The  heat  evolved  from  a 
starving  dog  at  a  temperature  of  33°  is  measured  by  placing  the 
animal  in  a  calorimeter.  Sufficient  food  is  then  given  to  supply 
an  amount  of  available  energy  equal  to  that  lost  daily  while 
starving,  and  the  heat  liberated  is  again  measured.  Any  increase 


UTILIZATION   OF   FOOD  421 

in  the  amount  of  heat  evolved  is  due  to  processes  essential  to  the 
digestion  of  the  food,  since  at  33°  no  heat  is  required  to  maintain 
the  body  temperature  of  the  animal.  The  heat  evolved  during 
starvation  being  put  at  100,  the  heat  evolved  during  the  same 
length  of  time  when  food  containing  an  equal  amount  of  available 
energy  (100)  was  fed  was  found  by  experiments  of  Rubner1  to 
be  as  follows : 

Heat  evolved 
in  starvation  100 

Heat  when  100  calories  flesh  was  fed 130.9 

Heat  when  100  calories  fat  was  fed 112.7 

Heat  when  100  calories  gluten  was  fed 1 28.0 

Heat  when  100  calories  cane  sugar  was  fed 105.8 

That  is  to  say,  the  consumption  of  the  food  caused  an  in- 
creased production  of  heat,  which  was  probably  due  to  digestion 
of  the  food.  Since  100  calories  of  available  energy  was  fed,  the 
increased  quantity  of  heat  evolved  represents  heat  evolved  by  the 
digestion;  that  is,  the  percentage  of  thermal  energy  contained  in 
the  available  energy.  This  ranged  from  5.8  per  cent,  with  the 
sugar  to  30.9  per  cent,  with  the  flesh. 

The  second  method  is  applicable  to  herbivorous  animals,  but 
gives  only  indications.  The  animal  is  fed  on  a  ration,  and  the 
heat  evolved  from  the  body  is  measured.  The  feed  to  be 
studied  is  added  to  the  ration  and  the  heat  is  again  determined. 
The  increase  in  heat  is  due  to  the  digestion  of  the  added  feed. 

The  following  figures  of  Armsby2  afford  an  illustration : 


Heat  in 
feed  digested 

Heat  produced 
by  animal 

Period  I  

6  618 

9067 

Period  II  

Q  482 

IO  206 

+  2,864 

4-1,139 

An  increase  of  2,264  calories  in  the  digested  food  caused  an 
increase  of  1,139  calories  in  the  heat  given  off  by  the  animal. 
That  is,  about  34  per  cent,  of  the  energy  of  the  food  was  con- 
sumed in  digestive  processes. 

1  Quoted  by  Kellner,  Die  Ernahrung  d.  Niitztiere,  p.  105. 

2  Proc.  Soc.  Prom.  Agr.  Sci.,  1902,  p.  100. 


422  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  Productive  Value  of  a  Nutrient. — As  we  have  previously 
stated,  the  quantity  of  a  ration  in  excess  of  the  maintenance  re- 
quirements of  an  animal,  may  be  used  for  productive  purposes. 
If  the  animal  is  a  fattening  animal,  this  excess  may  be  used  for 
putting  on  fat. 

Kellner1  has  estimated  the  fat  produced  by  various  nutrients 
and  feeds  by  the  following  method.  With  the  aid  of  the  respira- 
tion apparatus,  he  determined  the  income  of  carbon  and  nitrogen 
in  the  food  fed  and  in  the  water,  and  the  outgo  in  the  urine,  the 
solid  and  the  gaseous  excrements,  and  so  ascertained  the  quantity 
of  the  fat  and  flesh  produced  by  a  basal  ration  (Period  I).  This 
ration  was  sufficient  to  maintain  the  animal  and  produce  a  little 
fat.  In  Period  II,  the  nutrient  or  food  to  be  tested,  was  added 
to  this  basal  ration  and  the  amount  of  flesh  and  fat  produced  was 
again  determined.  The  small  quantity  of  flesh  gained  or  lost 
was  in  each  case  calculated  to  the  quantity  of  fat  which  would 
contain  an  equal  amount  of  energy.  The  amount  of  fat  gained 
in  Period  II  less  the  amount  of  fat  gained  in  Period  I,  gives  the 
gain  of  fat  due  to  the  additional  food  or  nutrient  fed.  The 
quantity  of  fat  produced  by  100  grams  of  the  food  or  nutrient 
digested  was  then  calculated  from  this  data.  The  quantity  of 
fat  produced  should  be  in  proportion  to  the  kinetic  energy  of  the 
feed. 

'Experiments  were  first  made  with  pure  nutrients,  with  the 
following  results : 

Fat  produced  by 
100  grams  digested 

Cocoanut  oil 59.8 

Ether  extract  of  coarse  feeding  stuffs 47.4 

Ether  extract  of  grasses 52.6 

Starch    24.8 

Cane  sugar 18.8 

Lactic  acid o.o 

Crude  fiber  (paper  pulp) 25.3 

Proteids  (albumen) 24.8 

Pentosans not  determined 

1  Landw.  Versuchs-stat.,  1900,  p.  450.     See  also  Arnisby,  Bulletin  71, 
Pennsylvania  Station. 


UTILIZATION  OF  FOOD 


423 


Productive  Value  of  Feeds. — The  substances  thus  mentioned 
represent  the  various  groups  of  constituents  of  a  feeding- 
stuff.1  Kellner  determined  the  composition  and  digestibility  of 
a  number  of  feeding-stuffs,  and  calculated  the  quantity  of  fat 
which  each  could  produce,  based  upon  the  values  given  in  the 
preceding  table  for  the  digestible  nutrients.  The  following  is  an 
example  of  the  method  of  calculation  used : 

COTTONSEED  MEAI,. 


Digested 

Fat  pro- 
duced by 
i  gram 

Total  fat 

grams 

39-6 
13.0 

12.  1 

0.235 
0.598 
0.248 

grams 
9-30 

7-77 
3-00 

Fat  in  100  grams  •  •  • 

Carbohydrates  (including  crude  fiber) 

Calculated  total  for  100  grams 

—20.07 
19.62 

Found  by  experiment  

Thus  100  grams  of  cottonseed  meal  should  produce  20.07 
grams  fat  under  the  conditions  given.  We  will  term  this  the 
productive  value. 

If  the  value  of  a  feeding-stuff  for  producing  fat  is  in  propor- 
tion to  the  quantity  of  digested  nutrients  present,  i.  e.,  if  the 
digested  nitrogen-free  extract  etc.,  of  one  feed  has  the  same 
value  as  that  of  any  other  (as  has  heretofore  been  assumed),  then 
the  above  method  of  calculation  should  be  correct. 

The  results  of  a  number  of  experiments  and  calculations  are 
given  in  table  on  following  page:2 

The  calculated  quantity  of  fat  is,  in  many  cases,  much  greater 
than  that  actually  found  by  experiment.  That  is  to  say,  the  pro- 
ductive value  of  different  kinds  of  feeds  is  not  necessarily  in  pro- 
portion to  their  content  of  digestible  nutrients. 

1  See  also  Hagemann,  Exp.  Sta.  Record  10,  p.  907. 

1  After  Kellner,  Die  Ernahrung  d.  Landw.  Niitztiere,  p.  163. 


424 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


FAT  PRODUCED  BY  100  GRAMS  OF  THE  FEEDS  NAMFD. 


Calculated 

from  digested 

nutrients 


Found  by 
experiment 


Percentage 
of  calculated 


Peanut  meal 18.9 

Palm  nut  meal 17.9 

Linseed  cake  meal 19.7 

Rice  meal 16.8 

Rye  meal 18.1 

Bean  meal 17.3 

Rye  bran 15.8 

Wheat  bran 15.4 

Brewers  grain  (dry  ^ 15.4 

Potatoes 18.5 

Sugar  beets 15.0 

Beet  residue  ( wet )    18.  i 

Beet  residue  ( dried ) 18.  i 

Wheat  straw,  I 10.4 

Wheat  straw,  II 8.4 

Oat  straw 10.9 

Barley  straw 11.7 

Meadow  hay,  I 12.9 

Meadow  hay,  II 15.6 

Clover  hay 12.4 

Grass  hay 13.3 


18.9 
18.3 
19.2 

18.3 
16.9 

16.3 
12.5 
ii.  9 
13.0 
18.1 

13-1 
17.4 

14.2 

2.1 
2.4 

6.6 

7-8 
8.1 
10.9 
8-5 
8-5 


100 

102 

98 

1 08 

93 
94 
79 
77 
84 
98 
87 
94 
78 

20 
29 

59 
64 

54 
55 
63 
64 


Relation  to  Character  of  Feed. — The  production  of  fat  from 
the  oil  meals,  potatoes,  and  rice  meal  was  equal  to  that  calculated. 
With  rye  meal  and  bean  meal  it  was  about  94  per  cent.  The 
beans  and  dried  beet  residues  were  deficient  to  the  extent  of  21 
to  23  per  cent.  The  values  of  none  of  the  concentrated  feed-stuffs 
fell  below  77  per  cent,  of  the  calculated. 

The  fat  production  found  to  take  place  with  the  hays  and 
straws  was  20  to  64  per  cent,  of  the  calculated  quantity.  The  de- 
ficiency was  found  to  be  related  to  the  total  quantity  of  crude 
fiber  in  the  feed.  For  example,  100  grams  of  wheat  straw  No.  I 
produced  8.3  grams  less  of  fat  than  the  calculated  quantity,  and 
contained  46.6  grams  of  crude  fiber ;  that  is,  there  was  a  deficit  of 
0.18  gram  of  fat  for  each  gram  of  crude  fiber  present.  For 
eight  straws  and  hays,  the  maximum  deficiency  of  fat  per  i  gram 
of  crude  fiber  present  was  o.iS  gram,  the  minimum  being  o.n, 
and  the  average  0.14  grams. 

This  deficiency  is  in  part  due  to  the  work  of  chewing  the  feed. 
A  number  of  experiments  were  repeated  after  grinding  the  feed, 


UTILIZATION  OF  FOOD  425 

with  the  result  that  the  average  deficit  was  found  to  be  only  0.073 
gram  of  fat  per  i  gram  of  crude  fiber  fed.  The  deficiency  was 
no  doubt  due  in  part  to  the  character  of  the  nitrogen-free  extract 
of  hays  and  straws,  which,  as  is  well  known,  is  not  composed  of 
sugars  and  starch,  but  largely  of  substances  hard  to  dissolve  and 
in  part  of  unknown  nature.  They  are  not  the  same  as  the  starch 
used  by  Kellner  to  represent  the  pure  nutrient. 

Calculating  Productive  Value. — Knowing  the  composition  and 
coefficient  of  digestibility,  the  productive  value  in  terms  of  fat 
of  a  given  feeding-stuff  may  be  calculated  so  as  to  be  in  accord 
with  the  experimental  work  cited.  The  results  are  expressed  in 
pounds  fat  which  may  be  produced  by  100  pounds  of  feed. 

Concentrated  Feeding-Stuffs. — Multiply  digestible  proteids  in 
100  pounds  fed  by  0.235.  Multiply  digestible  fat  by  0.598. 
Multiply  digestible  nitrogen-free  extract  and  crude  fiber,  taken 
together,  by  0.25.  Add  the  products,  and  multiply  by  the  per- 
centage of  fat  produced  by  the  feeding-stuff  in  question  as  per 
preceding  table.  If  the  feeding-stuff  is  not  named  in  the  table,  it 
will  be  necessary  to  use  the  factor  for  the  feed  most  closely 
resembling  it.  The  result  is  approximately  the  productive 
value  in  terms  of  fat.  Chaff,  rice  hulls,  and  other  by-products 
high  in  crude  fiber  are  not  considered  as  being  concentrated  feed- 
ing-stuffs. 

Roughage. — Proceed  as  directed  above,  using  the  factor  0.526 
for  digestible  ether  extract  in  grasses,  and  0.474  for  all  other 
roughages,  and  sum  up  the  fat  values  of  the  nutrients.  Then,  if 
the  roughage  is  not  ground,  multiply  the  total  quantity  of 
crude  fiber  present  in  100  pounds  by  0.14  and  subtract  this  quan- 
tity from  the  sum.  If  the  roughage  is  ground,  multiply  the  crude 
fiber  by  0.07  and  proceed  as  before.  With  green  feeds  contain- 
ing 8  per  cent,  or  less  crude  fiber,  deduct  0.085  gram  fat  for  each 
gram  of  crude  fiber;  with  those  containing  8  to  10  per  cent., 
deduct  0.095 ;  with  those  containing  10  to  12  per  cent.,  deduct 
0.108;  with  those  containing  12  to  14  per  cent,  deduct  0.12;  14 
to  16  per  cent.,  deduct  0.135;  over  J6  per  cent.,  deduct  0.14. 
28 


426  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  following  is  an  example  of  the  method  of  calculating  the 
fat  value  of  a  roughage : 

JOHNSON  GRASS  HAY  100  POUNDS. 

Digestible  protein 3-3  X    0.235        =    0.78 

Digestible  fat 0.7  X    0.474        =    0.33 

Digestible  crude  fiber 22.6 

Digestible  nitrogen-free  extract ...  28.  i 

~50.7  X  0.25  =  12.42 

Total 13.53 

Total  crude  fiber 38.0X0.14=    5.32 

Productive  value 8.21  pounds  fat 

This  means  that  100  pounds  of  the  Johnson  grass  hay  added  to 
a  ration  already  sufficient  to  maintain  the  animal,  should  produce 
8.21  pounds  fat.  The  fat  value  is  the  productive  value  for  fatten- 
ing, when  the  feed  is  used  for  fat  and  for  no  other  purpose. 

Kellner  expresses  the  productive  value  of  feeds  and  rations  in 
terms  of  starch;  that  is,  the  quantity  of  starch  which  is  capable 
of  producing  the  same  quantity  of  fat  as  100  pounds  of  the  feed 
is  capable  of  producing.  Armsby1  expresses  the  productive  value 
in  terms  of  heat  units  (therms).  There  are  two  objections  to 
this  manner  of  statement.  The  first  is,  that  the  heat  units  are 
used  for  the  total  heat  value  of  the  feed,  for  the  available  heat 
value,  and  for  the  productive  value,  introducing  some  confusion  in 
distinguishing  between  them.  The  second  objection  is,  that  the 
energy  equivalent  to  the  quantity  of  fat  produced  is  not  the  pro- 
ductive energy  of  the  feed,  since  no  doubt  some  of  the  energy 
must  be  consumed  in  the  process  of  transforming  the  nutrients 
into  fat.  The  productive  energy  may  be  proportional  to  the  fat 
produced,  but  is  not  identical  with  it. 

We  therefore  prefer  to  express  the  productive  value  of  feed 
in  terms  of  the  actual  experimental  basis,  namely,  of  the  fat 
which  they  were  found  to  produce. 

The  productive  value  of  a  feed  may  be  defined  as  the  quantity 
of  fat  which  the  feed  will  produce,  when  it  is  fed  in  addition  to  a 
ration  already  sufficient  to  supply  the  needs  of  the  animal  for 
maintenance. 

1  Farmers  Bulletin  No.  346. 


UTILIZATION  OF  FOOD  427 

Significance  of  the  Pjoductive  Value. — We  have  seen  that  a 
portion  of  the  value  of  a  food  is  lost  in  undigested  material,  a 
part  as  marsh  gas,  or  oxidized  in  fermentation,  a  part  in  the  in- 
completely oxidized  material  of  the  urine,  and  a  portion  is  used 
for  digestion  and  other  processes  fitting  it  for  the  use  of  animal. 
What  remains  of  the  food  after  these  losses  are  deducted,  may  be 
used  for  maintenance,  work,  fat,  flesh,  milk,  etc.  It  represents 
the  net  value  of  the  food  to  the  animal.  It  also  corresponds  to 
what  we  elsewhere  termed  the  kinetic  energy  of  the  food. 

The  productive  value  of  a  food  is  the  best  measure  so  far 
devised  for  the  net  value  of  a  food.  Rations  have  heretofore 
been  calculated  on  the  assumption  that  all  digestible  nutrients  of 
the  same  group  have  the  same  value  to  the  animal,  regardless  of 
the  origin  of  the  material.  We  now  know,  however,  that  the  net 
value  of  a  food  may  vary  widely  from  its  value  based  entirely  on 
digestible  nutrients,  so  that  the  value  of  a  food  for  the  purpose 
of  producing  energy  is  best  measured  by  its  productive  value. 

It  is  quite  possible  that  the  kinetic  energy  of  different  feeds 
undergo  somewhat  different  losses  when  transformed  into  fat, 
so  that  the  quantity  of  fat  produced  may  not  be  the  most  exact 
possible  measure  of  the  net  values  of  feeds.  The  energy  used 
in  digestion  and  given  off  as  heat  may  also  prove  useful  under 
certain  circumstances,  such  as  with  an  animal  on  a  maintenance 
ration  in  cold  weather. 

While  the  fat  values  of  feeding-stuffs  probably  represent  their 
comparative  values  for  fattening  purposes,  and  perhaps  for  milk, 
it  does  not  follow  that  they  represent  the  values  of  the  feeds  for 
productive  work  and  for  maintenance  of  the  animal.  The  con- 
version of  proteids,  etc.,  into  fat  undoubtedly  consumes  energy, 
and  a  greater  quantity  of  energy  may  be  required  to  convert  the 
proteids  of  one  feeding-stuff  into  fat,  than  those  of  another; 
whereas  if  the  kinetic  energy  is  used  directly  for  work  or  main- 
tenance, these  proteids  might  be  equal  in  value  for  these  pur- 
poses. We  have  seen  that  a  feeding-stuff  possesses  both  kinetic 
and  thermal  energy,  and  that  the  thermal  energy  may  be  used  to 
keep  the  animal  warm.  While  the  thermal  energy  fed  to  an 


428  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

animal  on  a  heavy  ration  may  be  so  excessive  that  differences  in 
the  thermal  energy  of  feeds  may  have  no  significance,  an  animal 
on  a  small  or  maintenance  ration,  may  be  able  to  utilize  the 
thermal  energy. 

The  use  of  the  productive  value  of  a  feed  is  no  doubt  a  decided 
advance  in  the  science  of  animal  nutrition,  as  it  emphasizes  the 
differences  in  the  productive  values  of  the  digested  nutrients  of 
different  classes  of  feeds.  It  is  clear  that  the  digested  nitrogen- 
free  extract,  for  example,  of  hays  and  fodders,  does  not  have  the 
same  value  to  the  animal  as  that  of  grains  and  other  concentrates. 

The  value  of  a  feed  for  nutrition  is  thus  indicated  by : 

1 i )  Its  content  of  digestible  protein,  or  power  to  produce  flesh. 

(2)  Its  productive  value  in  terms  of  fat,  or  its  power  to  pro- 
duce fat. 

Mineral  Materials. — Animals  require  inorganic  as  well  as 
organic  materials.1  The  term  "inorganic"  is  not  strictly  accurate 
when  used  in  connection  with  phosphates,  as  the  phosphorus  is 
partly  in  organic  combination.  However,  any  addition  of  phos- 
phates to  the  ration  is  made  as  inorganic  substances.  Ash  is  left 
by  all  organs  of  the  body  when  burned,  and  mineral  matter  ap- 
pears essential  to  their  proper  growth  and  development.  Mineral 
substances  are  required  in  processes  of  digestion  and  metabolism. 
Animals  fed  on  food  from  which  the  ash  has  beeen  extracted  be- 
come irritable,  nervous,  show  weakness  of  the  extremities,  and 
die  sooner  than  if  not  fed  at  all. 

The  most  important  inorganic  substances  are  salt,  phosphoric 
acid,  and  lime.  Salt  is  found  in  the  digestive  juices.  In  moderate 
amounts,  it  appears  to  favor  the  retention  of  proteids  by  the 
body.  Cattle  of  average  weight  should  receive  20  to  25  grams; 
sheep  and  pigs,  4  to  8  grams;  and  horses,  15  to  25  grams  per  day. 
With  heavy  rations  of  difficulty  digestible  foods,  cattle  may  re- 
ceive as  much  as  80  grams;  sheep,  12  grams;  and  pigs,  15  grams 
per  day.  An  excess  of  salt  increases  the  consumption  of  water, 
and  is  undesirable.  It  is  best  to  mix  the  salt  with  the  food. 
1  See  Ohio  Bulletin  No.  207. 


UTILIZATION  OF  FOOD 


429 


B 

Fig.  88.  — Maud  in  her  normal  condition  (A)  and  after  nine  months 
without  salt  (B).     Wisconsin  Station. 


43°  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Phosphoric  acid  is  found  in  the  flesh.  The  animal  takes  up 
phosphoric  acid  when  it  adds  flesh,  and  it  gives  off  phosphoric 
acid  when  it  loses  flesh.  Phosphoric  acid  is  also  found  in  the 
bones,  as  phosphates  of  lime  and  magnesia.  Phosphates  are  also 
present  in  milk. 

An  animal  which  does  not  receive  enough  phosphoric  acid, 
lime,  and  magnesia  in  its  food,  loses  continually  small  quantities 
of  phosphates  of  lime  and  magnesia.  This  is  removed  from  its 


Fig.  89.— Pens  used  in  feeding  experiments.     Illinois  Station. 

bones,  making  the  bones  porous,  weak,  and  liable  to  break.  This 
diseased  condition  occurs  in  some  districts  where  the '  feeding- 
stuffs  do  not  contain  enough  lime  or  phosphoric  acid,  and  may 
be  produced  artificially  by  withholding  phosphates  from  the 
animal.  It  may  also  be  caused  by  an  excess  of  acid  in  the  food. 
Growing  animals  which  do  not  receive  sufficient  lime  and  phos- 
phoric acid  quickly  suffer.  Movement  becomes  painful  to  them, 


UTILIZATION  OF  FOOD  431 

the  limbs  and  spinal  column  bend,  the  teeth  remain  small  and 
loose,  and  the  bones  weak.  Pigs  especially  are  liable  to  suffer  in 
this  way  because  the  potatoes  and  cereals  fed  to  them  do  not  con- 
tain enough  lime.1  Straw  and  chaff  of  cereals,  the  cereal  grains, 
and  their  by-products,  as  bran,  gluten  meal,  etc.,  malt  sprouts, 
molasses,  and  whey,  are  poor  in  lime.  The  straw  and  chaff  of 
grains,  beet  pulp,  potato  pulp,  and  molasses  are  poor  in  phos- 
phoric acid.  Clovers,  meadow  hay,  and  leguminous  seeds  are 
rich  in  lime.  Cereal  grains,  bran,  oil  cake,  flesh,  and  fish  by- 
products are  rich  in  phosphoric  acid. 

When  lime  is  deficient  in  the  feed,  it  may  be  supplied  as  pre- 
cipitated chalk.  Lime  and  phosphoric  acid  together  may  be  given 
in  the  form  of  precipitated  phosphate  of  lime  or  finely  ground 
bone. 

Lecithin2  appears  to  stimulate  the  growth  of  the  bones  and 
body.  For  example,  one  guinea  pig  fed  o.io  gram  lecithin  per 
day,  in  addition  to  other  food,  increased  1,380  grams  in  10  weeks; 
but  another  pig  fed  no  lecithin,  under  the  same  conditions,  gained 
300  grams.3 

Water. — Water  lightens  the  work  of  chewing,  and  makes  swal- 
lowing possible.  It  is  indispensable  to  digestion  and  absorption 
of  food.  The  digestive  ferments  can  act  only  in  solution,  and 
the  products  of  digestion  can  enter  the  body  in  dilute  solution 
only.  Concentrated  solutions  cause  strong  peristaltic  move- 
ments, which  end  with  the  ejection  of  the  material.  Water  also 
circulates  in  the  blood  and  secretions,  and  carries  out  the  ex- 
creted metabolic  products  in  the  urine.  It  aids  to  remove  an 
excess  of  heat  from  the  body  by  evaporation.  One  gram  of 
water  on  being  converted  from  the  liquid  to  the  gaseous  state 
takes  up  535.9  calories. 

Too  little  water  delays  digestion  and  absorption,  and  causes 
the  nitrogenous  metabolic  products  to  remain  in  the  body  longer 
than  usual.  The  blood  gradually  thickens,  the  body  temperature 
is  elevated,  and  the  decomposition  of  fat  and  albumen  con- 

1  See  Missouri  Bulletin  No.  6. 

2  Missouri  Bulletin  No.  61. 

3  Compt.  rendu.,  1902,  p.  1166. 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Fig.  90.— Calf  (A)  from  cowfedon  corn  products,  activeat  birth;  calf  (B)  from 
cow  fed  on  wheat  products,  unable  to  stand  at  birth.    Wisconsin  Station. 


Fig.  91. — Cow  (A)  fed  on  corn  products,  vigorous;  compare  with  cow  (B) 
fed  on  wheat  products,  unthrifty.     Wisconsin  Station. 


434  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

sequently  increases.  Growing  animals  are  injured  by  too  little 
water,  or  by  receiving  it  at  irregular  intervals.  When  water  is 
placed  freely  at  the  disposal  of  the  animal,  an  excessive 
consumption  is  not  to  be  feared,  unless  caused  by  very  watery 
food  or  too  much  salt.  The  amount  of  water  taken  up  on  an 
average  for  one  pound  dry  matter  is  as  follows : 

Pounds 

Swine 7  to  8 

Cows 4  to  6 

Oxen 2  to  3 

Horses    2  to  3 

Sheep   2  to  3 

The  quantity  of  water  consumed  varies  with  the  temperature,  as  in 
warm  weather  more  is  required  to  replace  that  lost  in  perspiration. 

Aromatic  Bodies. — These  are  the  bodies  which  give  an  agree- 
able taste  and  odor  to  feeding-stuffs.  They  have  no  effect  upon 
digestion,  and,  on  account  of  their  small  quantity,  little  on  pro- 
duction. Their  chief  effect  is  upon  the  nervous  system.  They 
awaken  the  appetite,  and  increase  the  activity  of  the  secreting 
organs  of  the  mouth  and  stomach.  Special  additions  of  aromatics 
are  not  necessary  when  good  hay,  sound  grain,  by-products  of 
milling,  oil  cakes,  or  even  good  stray  or  chaff  is  fed,  for  these 
contain  in  themselves  sufficient  appetizers. 

Rations  from  Eestricted  Sources. — Experiments  at  the  Wiscon- 
sin Experiment  Station,1  covering  a  period  of  four  years,  show 
that  animals  fed  rations  properly  balanced,  from  different  plant 
sources,  were  not  alike  in  general  vigor,  size,  and  strength  of  off- 
spring, and  capacity  for  milk  secretion.  Animals  fed  from  the 
products  of  the  wheat  plant  exclusively  were  deficient  in  vigor ; 
those  fed  from  the  corn  plant  were  strong  and  vigorous ;  those  fed 
from  the  oat  plant  were  not  as  vigorous  as  those  fed  the  corn 
plant ;  while  those  fed  a  mixed  ration  were  intermediate  between 
the  wheat  and  oat  rations  in  vigor.  The  significance  of  these  in- 
vestigations is  not  yet  apparent. 
1  Research  Bulletin  No.  17. 


CHAPTER  XXI. 


MAINTENANCE  RATION  AND  FATTENING. 

Maintenance  Ration. — The  amount  of  food  required  to  main- 
tain an  animal  is  called  the  maintenance  ration*  A  maintenance 
ration  must  provide  enough  energy  to  keep  up  the  body  heat,  and 
to  supply  the  digestive  and  vital  processes,  and  enough  proteids 
to  replace  the  body  waste,  and  provide  for  natural  growth  of 
hair,  horn,  etc.  The  amount  of  body  heat  required  will  depend 
upon  the  surrounding  temperature.  At  about  33°  C.  none  will 
be  required;  the  amount  necessary  at  lower  temperatures  will 
depend  upon  the  size  and  shape  of  the  animal,  its  protective 
coverings,  the  quantity  and  temperature  of  the  drinking  water, 
etc. 

Value  of  Food  for  Maintenance. — The  quantity  of  body  sub- 
stance protected  by  given  amount  of  food  may  be  estimated  as 
follows : 

Determine  the  income  and  outgo  of  carbon  and  nitrogen  of  the 
starving  animal.  Feed  the  nutrient  to  be  tested,  and  again  deter- 
mine income  and  outgo  of  the  carbon  and  nitrogen.  The 
amount  of  body  fat  and  flesh  protected  by  the  known  amount  of 
nutrients  fed  is  thus  ascertained. 

For  example,  the  following  is  an  experiment  of  Rubner:2 


Nitrogen 
eliminated 
per  day 

Fat 
decomposed 
per  day 

grams 

3-16 
20.63 

grams 

75-92 

30,72 

+1747 

—45-20 

The  meat  fed  increased  the  elimination  of  nitrogen  and  de- 
creased the  destruction  of  fat. 

The   meat   equivalent   to    17.47   grams   of   nitrogen    (  =  113.4 

1  Armsby,  Bulletin  No.  42,  Pennsylvania  Station. 

2  Zeitsch  f.  Biol.,  1886,  p.  04. 


43^  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

grams  dry  meat)  protected  45.2  grams  body  fat  from  oxidation, 
so  that  250  grams  dry  meat  would  protect  100  grams  of  fat.  But 
the  available  energy  of  water-free  meat  is  404  calories ;  and  that 
of  dog  fat  is  940  calories,  so  that  100  grams  fat  has  the  same 
heat  value  as  232  grams  of  meat,  and  the  meat  protected  body  fat 
approximately  in  proportion  to  its  available  energy. 

Similar  experiments  with  sugar,  starch,  and  other  nutrients 
have  shown  that  the  value  of  different  nutrients  to  an  animal 
that  is  fed  insufficient  food  are  in  proportion  to  their  content  of 
available  energy.  This  is  known  as  the  law  of  isodynamic 
replacement  of  nutrients.  This  law  holds  only  when  the  thermal 
energy  of  the  food  can  be  entirely  utilized  in  maintaining  the 
temperature  of  the  body.  When  the  thermal  energy  is  of  no 
value,  as  when  the  surrounding  temperature  is  the  same  as  that 
of  the  body,  nutrients  should  replace  one  another  only  in  propor- 
tion to  their  content  of  kinetic  energy.  (See  Chapter  XX). 
When  the  thermal  energy  is  only  partially  utilized,  the  law  is 
only  partly  true. 

Carnivorous  animals  may  be  maintained  on  a  ration  consisting 
of  flesh  alone.  The  quantity  necessary  is  between  three  and  four 
times  as  much  as  that  oxidized  by  a  starving  animal.  An  addi- 
tion of  fat,  sugar,  starch,  or  crude  fiber  decreases  the  amount  of 
proteids  required. 

Ascertaining  the  Maintenance  Ration. — The  ration  which  will 
keep  an  animal  without  loss  or  gain  of  fat  or  flesh  is  termed  the 
maintenance  ration.  The  maintenance  ration  is  ascertained 
exactly  by  feeding  an  animal  on  a  given  ration,  and  determining 
the  loss  or  gain  of  flesh  and  fat  by  means  of  the  carbon  and 
nitrogen  balance.  The  protein  and  non-protein  in  the  ration  are 
decreased,  or  increased,  as  appears  necessary  from  the  previous 
experiment,  and  the  carbon  and  nitrogen  balance  again 
determined.  That  ration  which  produces  only  a  very  slight  gain 
of  flesh  and  fat  is  considered  to  be  the  maintenance  ration.  It  is 
practically  impossible  to  feed  a  ration  which  does  not  produce 
either  a  slight  gain  or  loss. 


MAINTENANCE   RATION   AND    FATTENINGS  437 

Factors  which  Affect  the  Maintenance  Ration. — The  size  of  the 
maintenance  ration  is  affected  by  several  factors  in  addition  to 
the  vital  needs  of  the  animal. 

External  Temperature. — When  the  atmosphere  has  the  same 
temperature 'as  the  animal  body,  no  heat  is  required  to  keep  the 
animal  warm.  The  thermal  energy  of  the  food,  produced  in 
digestion,  will  maintain  the  animal  heat  for  a  few  degrees  below 
33°,  which  will  vary  according  to  the  character  of  the  food.  At 
lower  temperatures,  food  must  be  oxidized  to  keep  the  animal 
warm.  The  amount  of  food  so  required  will  depend  upon  the 
temperature,  and  other  factors.  For  example,  Rubner1  found 
the  heat  given  off  by  a  starving  dog,  is  measured  directly  in  a 
calorimeter,  to  be  as  follows : 

Temperature  Heat  evolved 

Degrees  C.  Calories 

7.6 86.4 

15-0 63.0 

20.O 56.0 

25-0 54-0 

30.0 56.0 

35-0 68.5 

About  65  per  cent,  more  energy  was  used  at  7.6°  C.  than  at 
25°.  At  35°  the  elimination  of  heat  is  increased,  probably  owing 
to  disturbances  due  to  the  high  temperature. 

Feeding  standards  are  based  on  a  temperature  of  15°  to  20°  C. 
At  higher  temperatures,  less  feed  will  be  required,  at  lower  tem- 
peratures, more.  Since  small  individuals  have  a  proportionally 
larger  body  surface  than  the  large  animals,  they  give  off  more 
heat,  and  so  require  more  food.  For  example,  it  is  estimated 
that  a  grown  steer  weighing  300  pounds  would  require  per  100 
pounds  weight,  food  of  0.19  pounds  fat  value,  while  a  steer  of 
800  pounds,  requires  per  100  pounds  weight,  food  of  0.14  pounds 
fat  value,  or  one-fourth  less,  weight  for  weight. 

The  Condition  of  the  Animal. — The  fatter  the  animal,  the 
more  food  it  requires  for  maintenance.  The  increased  food 
required  is  not  in  proportion  to  the  gain  in  weight,  but  the  pro- 
1  Gesetz  d.  Energieverbrauch,  1902,  p.  105. 


438  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

portion  is  greater  than  the  gain,  and  increases  as  the  animal  be- 
comes fatter. 

Temperature  of  Drinking  Water. — Water  consumed  must 
have  its  temperature  raised  to  the  temperature  of  the  animal 
body.  That,  of  course,  requires  heat,  the  amount  required  being 
considerable  if  the  water  is  cold.  For  an  example,  an  ox  weigh- 
ing 1,000  pounds  requires  for  maintenance,  food  having  the  pro- 
ductive value  of  750  grams  fat  per  day.  Such  an  animal  may 
consume  50  kg.  water  per  day.  If  this  water  has  the  temperature 
of  5°  C.  the  temperature  must  be  raised  to  39°,  that  is,  34°,  and 
the  heat  required  is  34  x  50  =  1,700  calories,  which  is  equal  to 
about  190  grams  fat.  This  is  about  25  per  cent,  of  the  main- 
tenance ration.  Cold  drinking  water  must  thus  be  compensated 
for  by  more  feed. 

Value  of  Protein  for  Maintenance. — Proteids  alone  will  main- 
tain the  animal  body.  The  quantity  of  proteids  required  is  con- 
siderably in  excess  of  the  amount  of  body  proteids  oxidized  by  a 
starving  animal.  By  experiments  on  dogs,  starved,  and  then  fed 
on  lean  meat,  it  has  been  found  that  for  100  parts  body  proteids 
oxidized,  369  parts  proteids  in  lean  meat  must  be  consumed  to 
maintain  equilibrium. 

The  proteids  in  the  body  are  in  two  forms,  circulatory  and 
body  proteids.  The  circulatory  proteids  are  rapidly  oxidized, 
while  the  body  proteids  are  much  more  resistant.  Thus,  the 
amount  of  proteids  oxidized  by  a  starving  animal  will  depend  at 
first  upon  the  quantity  of  circulatory  proteids  in  the  animal, 
which  in  turn  depends  upon  the  quantity  of  proteids  previously 
fed.  The  quantity  of  proteids  oxidized  while  an  animal  is 
starving,  rapidly  decreases  until  it  becomes  nearly  constant. 

The  amount  of  proteids  destroyed  the  first  day  depends  upon 
the  previous  ration,  but  after  the  fifth  day  it  becomes  nearly 
constant. 

Ammonium  acetate,  asparagin,  and  other  nitrogenous,  non- 
proteid  bodies,  have  little  or  no  value  for  maintenance.  An 
animal  fed  upon  them,  together  with  starch,  fat,  etc.,  will  starve 
to  death  for  want  of  proteids. 


MAINTENANCE:  RATION  AND  BATTENINGS 


439 


Value  of  Non-Protein  for  Maintenance. — Non-protein  nutrients, 
such  as  sugar,  starch,  fat,  etc.,  fed  alone,  will  decrease  the  destruc- 
tion of  body  proteids  by  a  starving  animal  to  a  certain  extent,  but 
not  entirely,  and  the  animal  will  starve  if  so  fed.  A  certain 
quantity  of  proteids  is  essential.  The  most  practical  maintenance 
ration  is  one  which  contains  both  protein  and  non-protein. 

Feeding  for  Maintenance. — Work  animals  may  be  placed  on 
maintenance  rations  during  periods  of  idleness;  fat  cattle,  be- 
tween end  of  fattening  period  and  time  of  sale;  grown  animals, 
until  the  time  of  fattening  begins;  and  sheep  kept  for  wool. 
Young  animals,  cannot  be  placed  upon  a  maintenance  ration,  as 
a  gain  of  flesh  is  the  normal  condition  with  them. 

The  maintenance  ration  must  provide  sufficient  energy  and 
sufficient  proteids  for  replacement  of  flesh  and  fat,  and  the 
growth  of  hair,  horn,  skin,  and  hoofs.  It  must  be  adjusted  to 
the  size  and  condition  of  the  animal,  and  other  external  condi- 
tions, such  as  we  have  discussed. 

On  account  of  the  small  quantity  of  kinetic  energy  and  the 
relatively  high  amount  of  heat  required  for  maintenance,  and  also 
because  the  feed  should  be  bulky  in  order  to  satisfy  the  appetite 
of  the  animal  without  carrying  large  amounts  of  nutriment,  hays 
and  straws  may  be  largely  used. 

Standards  for  Maintenance. — The  following  are  the  amounts  of 
food  found  necessary  for  maintenance  per  day  and  per  1,000 
pounds  live  weight : 


Total  weight 
dry  matter 

Proteids 

Productive 
value 

Nutritive 
ratio 

Steers  . 

pounds 

pounds 
o  f\  o  8 

Sheep,  coarse  breeds.  .  . 
Sheep,  fine  breeds  
Fat  steers  •  •  •  

18-23 
20-26 

I.O 

1.2 

1.50 
2.08 
2.25 

1      9 
i     9 
i    8 

T        8 

1.75  ^.-^o 

These  standards  are  based  upon  experiments  such  as  those  just 
cited.  Sheep  must  receive  enough  protein  to  provide  for  growth 
of  wool.  Methods  for  calculating  rations  will  be  given  in  an- 


44O  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

other  chapter.     The  nutritive  ratio  given  in  the  table  is  the  ratio 
of  protein  to  non-protein,  and  not  of  proteids. 

Coarse  feeds  are  largely  used  for  maintenance  purposes.  As 
they  almost  invariably  contain  enough  phosphoric  acid  and  lime 
to  supply  the  needs  of  the  animal,  the  ash  needs  little  attention. 
Such  an  animal  requires  per  1,000  pounds  live  weight  about  45 
grams  of  lime  and  22  grams  of  phosphoric  acid  in  the  food. 

Utilization  of  Nutrients  for  Production  of  Fat. — The  object  of 
fattening  the  animal  is  to  finish  it  for  market.  Some  of  the  facts 
and  principles  upon  which  the  fattening  rations  are  based  will  be 
discussed.  Only  the  food  fed  in  excess  of  maintenance  require- 
ments may  be  used  in  fattening.  In  the  preceding  chapter,  we 
not  only  had  the  evidence  that  proteids,  crude  fiber,  fat,  and 
nitrogen-free  extract  could  furnish  fat,1  but  also  the  quantity  of 
fat  which  each  could  produce.  Other  methods  of  experiment 
have  been  used  to  ascertain  whether  the  nutrients  of  the  food 
may  be  used  for  the  production  of  fat. 

Hoffman2  fed  a  dog  (previously  starved  for  some  days)  on 
370.8  grams  of  fat,  and  49  grams  of  proteids  (lean  meat)  per 
day.  In  five  days  the  animal  gained  4.2  kilograms  and  then  con- 
tained 1352.7  grams  of  fat.  The  amount  of  fat  present  at  the  be- 
ginning of  feeding  was  estimated  at  150  grams  as  ascertained  by 
examination  of  the  dog.  The  maximum  quantity  that  could  have 
been  formed  from  the  proteids  fed  was  130.5  grams.  The  re- 
mainder of  the  fat,  at  least  1,072  grams,  must  have  come  from 
the  fat  eaten. 

The  following  experiments  of  Soxhlet3  show  that  carbo- 
hydrates may  form  fat.  Three  pigs  5  to  6  months  old  were  first 
fed  alike  for  321  days.  One  was  killed  then  and  the  body  sub- 
jected to  analysis  to  ascertain  its  fat  content.  The  remaining 
two  were  fed  on  steamed  rice  for  75  days  and  82  days, 
respectively,  the  nutrients  digested  being  determined  by  analysis 
of  food  and  excrement  as  in  digestion  experiments.  The  animals 

1  Soskin,  Exp.  Sta.  Record  8,  p.  179. 
-  Landw.  Versuchs-stat.,  1894.  p.  475. 
:i  Centralblatt  f.  Agr.  Chem.,  1 88 r,  p.  57.1. 


MAINTENANCE:  RATION  AND  FATTENINGS 


441 


were  then  killed  and  subjected  to  analysis.  A  quantity  of  fat 
equal  to  that  in  the  pig  first  killed  was  subtracted,  and  the  differ- 
ence assumed  to  represent  the  gain  in  fat.  The  results  of  the 
experiment  are  as  follows : 


Pig  No.  i 

Pig  No.  2 

kg. 

T  AA 

kg- 
I  60 

1.44 

o  89 

OA  r 

O  ^ 

TIC 

Fat  possible  from  proteids  decomposed  (assuming  pro- 

^•JJ 

I   78 

\  68 

Fat  in  food  fed  

O-7O 

^.VJ<-> 

O  ~\A. 

Total  fat  possible  from  proteids  and  fat  of  food  

2  08 

A    Q2 

Gain  of  fat  by  animal  

10  08 

22   l8 

8  oo 

18  16 

Thus,  after  allowing  for  the  greatest  possible  gain  of  fat  from 
the  proteids  and  the  fat  fed,  there  remains  a  large  quantity  of  fat 
which  could  come  only  from  the  carbohydrates.1 

The  fat  of  the  animal  has  been  found  to  be  modified  by  the  fat 
of  the  food  to  a  certain  degree.  In  one  experiment,  a  fat  con- 
taining iodine  was  fed,  and  was  found  in  the  body  fat,  and  also 
passed  into  the  milk.  A  portion  of  the  fat  of  the  food  may  be 
stored  in  the  animal.  The  body  fat  of  each  kind  of  animal 
possesses  characteristic  properties ;  the  cow  produces  only  cow 
fat;  the  dog,  dog  fat,  etc.  Under  ordinary  conditions,  only  a 
small  part  of  the  animal  fat  comes  directly  from  the  food ;  the 
major  portion  is  a  product  of  the  transformation  of  matter  in 
the  cells  of  the  animal.  Only  when  foods  rich  in  fat,  such  as  oil 
cake,  corn,  rice  bran,  etc.,  are  fed,  can  the  characteristics  of  the 
food  fat  be  observed  in  the  fat  of  the  body  or  of  the  milk.  It  is 
usually  the  custom  to  finish  the  animal  on  feed  which  will  give 
the  desired  characteristics.  The  fat  of  animals  fed  on  cereals 
and  grains  rich  in  carbohydrates  and  poor  in  oils,  is  hard.  A 
softer  fat  is  obtained  when  linseed  cake,  peas,  wheat  bran,  oats, 
etc.,  are  fed.  Animals  exposed  to  cold  have  a  softer  fat  than 
1  See  also  Bulletin  22,  p.  271,  Office  Exp.  Sta.,  U.  S.  Dept.  Agr. 
29 


442 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


those  kept  in  warmer  surroundings.  A  pig  kept  in  a  pen  at 
freezing  temperature  had  a  softer  fat  than  similar  pig  kept  in  a 
pen  at  30-35°  C. 

Composition  of  Gain  of  Weight  in  Fattening. — The  composition 
of  the  increased  weight  in  fattening  has  been  studied  in  two  ways : 

First,  animals  of  different  degrees  of  fatness,  but  otherwise 
comparable,  were  killed  and  subjected  to  analysis. 

Second,  animals  raised  alike  were  selected,  and  some  killed  at 
the  beginning,  others  at  intermediate  stages,  others  at  the  end  of 
the  fattening  experiment.  The  bodies  were  subjected  to  analysis. 

The  animals  killed  at  the  end  of  the  experiment  or  during  the 
process,  were  supposed  to  have  originally  had  the  same  composi- 
tion as  those  killed  at  the  beginning  of  the  experiment.  When 
the  live  weight  of  the  animals  and  their  percentage  composition  is 
known,  it  is  a  simple  matter  to  calculate  the  composition  of  gain 
in  material  during  fattening. 

The  composition  of  sheep  at  different  degrees  of  fatness  was 
found  at  Rothamsted1  to  be  as  follows : 

PERCENTAGE  COMPOSITION  OF  SHEEP. 


Lean 

Half  fat 

Fat 

Very  fat 

Offal 

6  n 

•       5  o 

Carcass 

14  8 

•l 
14  o 

122 

•* 

jo  Q 

f?of 

T»  7 

7C    6 

iv.y 

AS  8 

AcV| 

10.  / 

•^o-o 

32 

«5O-U 

2  8 

4o'° 
2  Q 

Water 

•• 

C7    7 

•* 

CQ  2 

A1  A 

**y 

TC  2 

O/-O 

4o-4 

6o"* 

Total  

IOO  O 

IOO  O 

IOO  O 

IOO  O 

It  is  noted  that  there  is  a  decided  decrease  in  the  percentage  of 
water,  a  slight  decrease  in  the  percentage  of  proteids,  and  a  large 
increase  in  the  percentage  of  fat,  during  the  process  of  the  fatten- 
ing. With  other  animals  than  sheep,  the  results  were  similar. 

The  following  table  shows  one  calculation  of  the  composition 
of  the  gain  in  fattening,  and  illustrates  the  method  of  procedure. 
The  part  of  the  offal  in  the  gain  is  calculated  also. 
1  Bulletin  22,  p.  249,  Office  Exp.  Sta.,  U.  S.  Dept.  Agr. 


MAINTENANCE   RATION   AND    BATTENINGS 


443 


COMPONENTS  OF  A  FAT  AND  A  LEAN  SHEEP,   SHOWING  THE 
COMPOSITION  OF  THE  GAIN  IN  FATTENING. 


Very  fat 
kg. 

I,ean 
kg. 

Gain 
kg. 

Percentage 
composition 
of  gain 

Total  weight 

108.6 

11.83 
49-74 
3-15 
38.23 
5-6o 

44-3 
6.56 
8.27 
I.4I 

25.38 
2.67 

64.3 
5.27 
41.47 

1.74 
12.85 

2-93 

100.0 
8.2 

64-5 
2.7 
2O.O 
A.6 

Kat 

Ash                 

Water      

Offal  .            

The  average  increase  in  body  substance  on  fattening,  exclusive 
of  offal,  from  the  experiments  on  oxen,  sheep,  and  swine  at  the 
Rothamsted  Experiment  Station  is  as  follows: 

Proteids 7.5 

Fat 66.6 

Mineral  matter 1.5 

Water 24.4 

IOO.O 

It  is  seen  that  the  increase  is  mostly  fat,  only  a  small  part  being 
proteids.  The  nutritive  ratio  of  this  gain  is  1 : 20.  These 
animals  were  not  entirely  grown.  Grown  animals,  if  in  fair  con- 
dition, gain  very  little  flesh  (proteids)  when  fattened. 

Factors  which  Influence  the  Fattening  Ration. — A  number  of 
factors  influence  the  fattening  ration: 

Requirements  for  Maintenance. — Since  only  the  excess  of  the 
productive  value  of  the  food  over  the  maintenance  requirements 
may  be  used  for  fattening,  anything  which  affects  the  mainten- 
ance requirements  will  affect  the  fattening  ration.  An  increase 
in  the  maintenance  requirements  will  decrease  the  gain  in  fat. 

Stall  Temperature. — On  account  of  the  heavy  ration  fed,  the 
animal  has  a  large  excess  of  thermal  energy,  and  the  temperature 
of  the  stall  may  fall  lower  than  when  fed  on  a  maintenance  ration 
without  affecting  the  amount  of  fat  gained.  But  if  the  stall  be- 
comes too  cold,  maintenance  requirements  are  increased  and  the 
animal  gains  less  fat.  If  the  animal  has  to  warm  the  water  con- 
sumed in  cold  weather  to  the  body  temperature,  the  maintenance 
requirements  may  be  considerably  raised.  A  large  proportion  of 
the  material  otherwise  available  for  fat  might  be  so  used.  It  has 


444  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

often  been  found  profitable  to  warm  the  drinking  water,  especially 
for  hogs. 

If  the  external  temperature  is  too  high,  the  animal  may  have 
trouble  in  disposing  of  the  heat  from  the  excess  of  thermal 
energy,  and  will  then  eat  less  of  the  ration.  For  this  reason 
fattening  in  summer  may  be  difficult ;  in  some  parts  of  the  South, 
animals  fatten  better  when  fed  out  of  doors  where  the  perspira- 
tion may  evaporate  freely,  than  when  confined.  It  is  also  often 
advisable  to  feed  light,  rather  than  heavy  fattening  rations  during 
warm  weather. 

Condition  of  Animal. — The  fatter  the  animal,  the  more  food 
required  for  maintenance,  and  the  less  the  proportion  of  it  avail- 
able for  fattening.  Thus  the  cost  of  the  production  of  fat  in- 
creases with  the  duration  of  the  fattening  process. 

Age  of  Animal. — South  Dakota1  experiments  show  the  follow- 
ing relation  between  feed  consumed  and  gain  in  weight,  for  cattle 
of  different  ages. 


Pounds  eaten  for  each  pound 
of  gain  in  live  weight 

Concentrates 

Hay 

Yearling  steers  

6.7 

7-9 

8.5 

4-3 
4.6 

Two-year-old  steers  

Excess  Over  Maintenance  Requirements. — Only  the  excess  of 
food  over  the  maintenance  requirement  can  be  used  for  produc- 
tion. The  larger  the  excess,  within  the  limit  of  the  ability  of  the 
animal  to  use  it,  the  more  economically  the  food  is  used.  For 
example,  if  a  steer  weighing  1,000  pounds  that  requires  1.5  pounds 
productive  value  for  maintenance,  is  fed  2.0  pounds,  then  only 
0.5  pounds,  or  one-fourth  of  the  ration  is  used  for  production  of 
fat.  But  this  animal  should  be  able  to  use  3.0  pounds  productive 
value,  and  in  such  case  1.5  pounds,  or  one-half  of  the  value  of  the 
food  is  used  for  fat.  The  fat  produced  by  the  first  ration  will 
require  twice  as  much  productive  value  as  that  formed  by  the 
1  Bulletin  No.  125. 


MAINTENANCE   RATION   AND   FATTENINGS 


445 


I 

5 

fe 


& 


I 


^ 
•< 


IK 

I 


s 


:? 


446 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


second.  The  second  ration  should  produce  the  same  results  in 
two  months  that  the  first  would  give  in  five.  In  the  latter  case 
there  is  not  only  a  greater  expenditure  for  food,  but  also  twice  as 
long  to  feed  and  care  for  the  animal. 

This  may  be  put  in  another  way.  Suppose  a  steer 
weighing  800  pounds  is  fed  on  5  pounds  cottonseed  meal  and  20 
pounds  cottonseed  hulls  per  day.  This  ration  would  have  a 
productive  value  of  1.55.  The  animal  would  have  a  maintenance 
requirement  of  1.2,  leaving  0.35  pound  for  fattening,  which 
would  produce  about  0.5  pound  gain  in  live  weight  per  day.  Sup- 
pose one  pound  corn  meal  is  substituted  for  one  pound  cotton- 
seed hulls.  The  ration  would  gain  0.17  pound  in  productive 
value,  which  should  cause  a  gain  of  about  0.25  pound  in  live 
weight  per  day.  An  addition  of  2  pounds  corn  meal  would  thus 
double  the  gain  in  weight  per  day. 

Too  heavy  a  fattening  ration  taxes  the  capacity  of  the  animal, 
and  decreases  the  production  of  fat.  The  excess  interferes  with 
the  digestive  processes  and  makes  the  fattening  less  successful. 
Experiments  have  shown  that  an  excessive  ration  does  not  pro- 
duce as  large  gains  as  a  ration  adapted  to  the  capacity  of  the 
animal.  The  following  are  results  of  two  series  of  experiments 
by  Morgan1  on  sheep,  in  which  the  quantity  of  protein  was  kept 
constant,  but  the  carbohydrates  were  increased.  The  effect  of 
the  increase  in  the  ration  is  to  decrease  the  gain  in  weight. 

DIGESTIBLE  NUTRIENTS  FED  PER  1,000  POUNDS  LIVE  WEIGHT. 


Protein 

Carbohydrates 

Daily  increase 
in  weight 

Experiment  i 

pounds 

pounds 
ifi  c 

pounds 
i  cfi 

•54 

1DO 
TQ  Q 

3-5° 
i  76 

Group  C   •'• 

oO4 

3-7° 

Experiment  2 
Group  A  

•04 

«;  18 

21.3 

18  i 

•79 

A     06 

^  18 

2O  7 

•*  8? 

OTOUD  O 

c   TS 

o-°/ 

J.  10 

•*J-J 

./u 

Quoted  by  Kellner,  Die  Ernahrung  d.  Landw.  Niitzture,  p.  414. 


MAINTENANCE:  RATION  AND  BATTENINGS  447 

Feeding  Experiments, — The  values  of  feeding-stuffs  for  fat 
production  are  often  compared  by  means  of  feeding  experiments. 
Feeding  experiments  have  also  been  of  great  value  in  establishing 
standards  of  feeding  for  various  purposes.  Feeding  experi- 
ments do  not  give  such  exact  values  as  experiments  in  which  the 
carbon  and  the  nitrogen  balance  are  determined,  but  they  are  very 
useful  in  their  proper  field. 

Two  systems  of  feeding  experiments  are  used.  In  the  first 
system,  the  same  groups  of  animals  are  fed  upon  the  different 
rations  in  succession.  The  method  is  open  to  the  objection  that 
the  effect  of  any  ration  will  depend  to  a  considerable  extent  upon 
the  preceding  rations,  and  the  same  feed  may  give  entirely  differ- 
ent results  according^to  the  character  of  the  feeding  which  precedes 
it.  The  feed,  of  course,  affects  the  condition  of  the  animal,  so  that 
the  maintenance  requirements  vary,  and  the  excess  of  the  ration 
over  the  maintenance  requirements,  which  is  the  portion  used  for 
the  gain  in  weight,  will  depend  upon  the  previous  feeding.  The 
results  of  the  feeding  will  thus  depend  upon  the  previous  feed, 
as  well  as  on  the  ration  being  studied. 

The  second  system  consists  in  dividing  the  animals  into  groups, 
and  feeding  to  the  different  groups  the  rations  to  be  compared. 
This  method  gives  good  results  when  properly  used.  Care 
should  be  exercised  to  have  the  groups  exactly  equivalent  at  the 
beginning  of  the  test.  The  groups  should  consist  of  10  or  more 
animals.  Each  animal  should  be  matched  in  age,  form,  live 
weight,  etc.,  with  another  animal  in  the  other  group.  The  groups 
should  be  compared  by  means  of  a  preliminary  feeding  period,  in 
which  the  animals  receive  the  same  ration  for  thirty  days  or 
more.  If  each  group  makes  the  same  gain  on  the  same  feed, 
the  experiment  proper  may  be  begun;  but  if  there  is  only  a 
slight  difference  in  gain,  the  groups  should  be  rearranged,  and 
another  test  made. 

The  best  results  are  secured  when  the  ration  is  about  three 
quarters  of  the  standards.  If  the  production  is  forced  to  its 
upper  limit,  or  if  more  feed  is  given  than  the  animal  can  utilize, 
the  differences,  due  to  the  different  feeds,  may  be  insignificant. 


448  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

When  different  feeds  are  added  to  a  basal  ration,  the  productive 
value  should  not  be  altered  by  other  compensatory  additions.  For 
example,  if  cottonseed  meal  is  compared  with  gluten  meal,  and 
straw  is  added  to  increase  the  nitrogen-free  extract  for  cotton- 
seed meal,  the  experiment  would  be  unfavorable  to  cottonseed 
meal,  because  the  nitrogen-free  extract  of  straw  is  not  equal  to 
that  of  gluten  meal.  The  rations  should  be  weighed  out  for  each 
animal,  and  fed  in  such  order  or  with  such  preparation  that  they 
will  be  completely  consumed. 

The  live  weight  varies  very  much  on  account  of  irregular  ex- 
cretion of  dung,  irregular  elimination  of  urine,  unequal  con- 
sumption of  water  from  day  to  day,  etc.  The  animals  should  be 
weighed  three  days  in  succession,  just  before  the  midday  meal, 
every  ten  days.  Since  the  first  weighings  are  usually  of  little 
value,  on  account  of  the  animals  being  excited,  the  animals  should 
be  accustomed  to  the  weighing  as  early  as  possible. 

The  feeding  period  should  not  be  too  short.  Two  months  is 
the  minimum  for  fattening  and  work  animals,  but  it  is  better 
to  continue  the  experiment  with  fattening  animals,  until  they  are 
fully  fat  and  then  to  make  a  slaughter  test  on  them.  Important 
observations  are  sometimes  made  only  when  the  experiment 
is  continued  a  long  time. 

When  comparing  two  feeds,  equal  quantities  should  be  fed.  If 
one  feed  is  more  palatable  than  the  other,  and  the  animals  allowed 
to  eat  more,  they  will  have  a  larger  excess  over  their  maintenance 
requirements,  and  the  results  will  be  more  favorable  to  the  more 
palatable  food. 

Standards  for  Fattening  Rations. — Since  fattening  animals  put 
on  little  flesh,  it  would  appear  that  they  require  little  more  pro- 
teids  than  animals  on  a  maintenance  ration.  The  heavy  ration 
fed,  however,  demands  a  quantity  of  digestive  fluids  composed 
largely  of  proteids.  Since  the  digestibility  of  the  food  is  de- 
creased if  the  nutritive  ratio  is  too  wide,  the  nutritive  ratio 
should  not  be  wider  than  1 :  10.  A  ratio  narrower  than  i :  4  in- 
creases the  oxidation  of  matter  in  the  body,  and  so  decreases  the 
production  of  fat.  Numbers  of  experiments  have  been  made 


MAINTENANCE:  RATION  AND  BATTENINGS 


449 


comparing  wide  and  narrow  rations.  Wolff,1  for  example,  taking 
the  average  of  18  experiments,  found  sheep  to  make  equal  gains 
whether  the  nutritive  ratio  was  i :  7  to  8,  or  1 :  4  to  5.  Lehmann2 
compared  i :  12  to  1:5,  with  equal  results.  There  is  thus  a 
wider  margin  in  the  quantity  of  digestible  protein  which  may  be 
fed,  and  if  protein  is  sufficiently  cheap,  it  may  be  used  for  the 
purpose  of  producing  fat. 

If  the  animal  is  not  in  good  condition,  the  ration  should  be 
moderate  at  first  and  gradually  increased,  beginning  with  a  nutri- 
tive ratio  not  wider  than  i :  6. 

The  quantity  of  fat  fed  is  not  important,  but  if  fed  to 
ruminants  in  greater  quantity  than  one  pound  per  1,000  pounds 
live  weight,  it  is  liable  to  decrease  the  appetite  or  cause  digestive 
disturbances  and  interfere  with  the  fattening.  Pigs  can  use  more 
than  this  amount. 

The  fattening  ration  for  steers  should  not  exceed  3.6  pounds 
productive  value  per  day  and  per  1,000  pounds,  but  may  be  lower 
than  this,  according  to  the  time  it  is  desired  to  take  for  the  fatten- 
ing. Rapid  fattening  is  less  expensive  than  slow  fattening.  The 
increase  in  live  weight  in  fattening  diminishes  in  the  course  of 
the  process,  since  the  maintenance  requirements  increase  with 
the  increase  in  weight  of  the  animals.  The  cost  of  production 
of  gain  in  weight  increases  considerably  towards  the  end  of  the 
fattening  period. 

The  following  are  the  amounts  of  nutrients  desirable  for  fat- 
tening, per  day  and  1,000  pounds  live  weight: 


Total 
weight  dry 
matter 

Proteids 

Productive 
value 

Nutritive 
ratio 

Pigs 

33-37 
28-33 
24-28 

24-32 

22-30 
24-32 
22-30 

3-0 

2.8 
2.0 

1.6 

1.8 
1.6 

1.4 

6.8 
6-5 
5-o 
3-6 

3-0 
3-0-3-6 
2.8-3.4 

i  :  5-5 
i  :  6.0 
1:6.5 

i  :4-5 

i  :  6.4 

i  :  5-5 
i  :  6.0 

Final  period  

Fattening  sheep  

Fattening  oxen 

1  Landw.  Jahrbuch,  1896,  p.  193. 

2  Landw.  Jahrbuch,  1902,  p.  162. 


45O  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

The  fattening  standard  calls  for  that  quantity  of  feed  which 
gives  the  most  rapid  fattening.  Any  excess  of  feed  over  the 
maintenance  requirements  produces  fat;  the  fattening  standard 
gives  the  largest  quantity  which  should  be  used. 

Practice  of  Fattening. — Straw  has  little  value  for  fattening 
purposes.  It  is  so  bulky  that  the  animal  cannot  eat  sufficient 
feed  for  best  results,  when  the  straw  is  used  in  quantity  in  the 
ration.  Even  good  meadow  or  clover  hay  has  too  great  bulk  in 
proportion  to  its  nutritive  content  to  be  used  in  quantity  in 
intensive  fattening.  Good  pasturage  is  excellent  for  fattening, 
and  in  exceptionally  favored  localities  may  be  the  only  fattening 
feed.  But  usually  the  animal  is  finished  on  more  concentrated 
feed. 


Fig.  93. — Carcass  of  hogs  fed  on,  (A)  corn  and,  (B)  barley. 
North  Dakota  Station. 

In  feeding  large  rations,  care  must  be  taken  to  render  the  food 
palatable,  so  that  the  animal  will  be  induced  to  eat  as  much  as 
possible.  The  use  of  well-flavored  feeds,  salt,  molasses,  or 
special  preparation  of  the  feed,  may  be  of  advantage  in  causing 
the  animal  to  consume  the  desired  amount. 


MAINTENANCE  RATION   AND   BATTENINGS  451 

Anything  that  disquiets  the  animal,  as  irregular  meals,  rough 
treatment,  insufficient  bedding,  etc.,  increases  the  oxidation  of 
matter  and  decreases  the  production  of  fat.  Armsby  has  found, 
by  direct  measurements,  that  an  animal  standing  consumes  about 
one-fourth  more  energy  than  when  lying  down.  The  temperature 
of  the  stall  should  be  kept  low  rather  than  high,  as  the  digestive 
processes  of  the  fattening  animal  evolve  a  considerable  amount  of 
heat,  which  is  partly  radiated  and  partly  carried  off  by  evapora- 
tion of  water  from  the  body.  If  insufficient  ventilation,  heavy 
hair,  or  fat  layers  under  the  skin  decrease  evaporation,  the  animal 
instinctively  consumes  less  food. 

The  effect  of  fattening  is  chiefly  perceptible  in  increase  of  live 
weight.  At  the  beginning,  the  weight  increases  rapidly  for  a 
few  days,  due  to  filling  the  body  with  food  and  water.  After  the 
fattening  proper  has  been  begun,  regular  weighings,  which  are 
best  made  before  the  morning  meal,  shows  the  progress  of  the 
fattening.  According  to  the  quantity  of  the  feed,  a  tolerably 
constant  increase  in  weight  occurs  for  a  longer  or  shorter  period. 
The  weekly  increase  then  gradually  becomes  less  and  less,  until 
finally  it  disappears.  When  the  increase  of  weight  ceases,  it 
does  not  prove  that  fattening  has  ceased.  Fat  continues  to  be 
deposited  for  a  time,  taking  the  place  of  water,  until  the  capacity 
of  the  tissues  is  satisfied.  The  cost  of  production  of  the  increase 
of  fat  and  flesh  increases  considerable  towards  the  end  of  the 
fattening  period. 

Another  cause  of  the  decreased  production  with  length  of  fat- 
tening period  is  the  increase  in  the  maintenance  requirement  of 
the  animal,  which  takes  place  more  rapidly  than  the  increase  in, 
weight. 

For  the  maintenance  of  fattening  animals,  rations  much  smaller 
than  the  fattening  ration  suffice,  and  should  depend  on  the  degree 
of  fatness.  The  transition  to  a  maintenance  ration  should  be 
gradual. 

'  Hogs  i-l/2  years  old  require  no  specially  high  amounts 
of  protein.  As  they  have  a  high  digestive  power  for 
carbohydrates  the  nutritive  ratio  may  be  as  wide  as  i :  10. 


452  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Excessive  quantities  of  fat  in  the  feed  may  injure  the  quality  of 
the  bacon.  At  the  beginning  of  the  fattening  period,  hogs  may 
consume  as  much  as  30  pounds  food  per  1,000  pounds  weight,  but 
as  the  fattening  progresses,  which  ends  in  3^  to  4  months,  the 
consumption  of  food  sinks  considerably,  until  towards  the  end,  19 
to  20  pounds  are  used.  The  ration  for  the  different  periods  of 
fattening  are  shown  in  the  table  previously  given. 

If  the  hogs  are  in  poor  condition,  a  preliminary  period  of  2  to 
4  weeks  with  4  pounds  proteids  is  advisable.  The  proteids  should 
also  be  increased  if  the  animals  are  not  fully  grown. 


CHAPTER  XXII. 


FEEDING  WORK  ANIMALS  AND  GROWING  ANIMALS. 

Work  requires  energy,  which  is  produced  by  the  oxidation  of 
organic  matter  within  the  tissues.  It  has  been  known  for  a  long 
time  that  animals  use  up  more  oxygen  and  give  off  more  carbon 
dioxide  while  they  are  doing  work  than  when  they  are  at  rest. 
A  considerable  amount  of  investigation  has  been  required  to 
ascertain  the  value  of  different  nutrients  for  producing  work. 

Nutrients  Oxidized  During  Work. — The  effect  of  work  upon 
the  proteids  of  the  body  can  be  studied  by  determining  the  quan- 
tity of  nitrogen  in  the  urine  during  periods  of  rest  and  periods 
of  work.  If  the  work  necessarily  involves  a  destruction  of  pro- 
teids, an  increased  elimination  of  nitrogen  will  result.  Experi- 
ments have  given  contradictory  results.  For  example,  a  dog  fed 
on  meat  eliminated  the  following  quantities  of  nitrogen,  during 
three  consecutive  periods : 

Nitrogen  in  urine 
grams  per  day 

No  work 54.9 

Working 48.6 

No  work 55.0 

In  other  experiments,  the  proteid  metabolism  was  considerably 
increased.  The  results  depend  on  the  ration  being  fed.  If  the 
ration  supplies  sufficient  carbohydrates  and  fat  to  furnish  energy 
for  the  work,  proteids  will  not  be  oxidized,  but  if  the  ration  is 
deficient  in  this  respect,  proteids  will  be  oxidized  to  furnish  the 
necessary  energy. 

Animals  at  work  exhale  increased  amounts  of  carbon  dioxide, 
even  though  there  be  no  increase  in  the  quantity  of  nitrogen 
eliminated.  This  is  evidence  that  fats  or  carbohydrates  are  be- 
ing used  for  the  production  of  work.  Further  evidence  that 
starch  and  other  non-proteids  can  be  used  for  the  production  of 
work,  is  afforded  by  experiments,  such  as  the  following: 

A  working  animal  was  fed  on  a  ration  poor  in  protein.  In 
a  second  period  the  same  ration  was  fed  with  the  addition  of 
starch  and  the  amount  of  work  was  then  increased  until  the 


K  was 


454  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

same  amount  of  nitrogen  was  eliminated  as  in  the  first  period. 
When  the  same  amount  of  protein  was  being  decomposed,  it  was 
found  that  the  animal  was  doing  more  work.  That  is,  the  starch 
was  used  for  production  of  work.  A  similar  experiment  showed 
that  oil  enabled  the  animal  to  do  more  work.  An  experiment 
showing  that  proteids  may  be  used  in  work  was  as  follows : 
A  horse  was  fed  a  ration  rich  in  protein,  and  put  on  light  work 
for  about  ten  days.  The  work  was  then  trebled,  being  a  hard 
day's  work.  The  excretion  of  nitrogen  immediately  increased  45 
grams  per  day,  and  the  live  weight  of  the  animal  gradually 
decreased. 

Exercise  may  cause  muscular  growth.  For  example,  Atwater 
and  Benedict  found  that  a  man  at  rest  lost  0.7  gram  nitro- 
gen per  day  and  7.8  grams  fat;  but  when  working,  he  gained  i.i 
gram  nitrogen  and  lost  48.4  grams  fat  on  the  same  ration. 

Respiratory  Methods. — The  following  is  a  method1  for  deter- 
mining the  consumption  of  energy  during  various  kinds  of  work, 
which  has  also  been  of  service  in  other  studies,  such  as  ascertain- 
ing the  amount  of  energy  involved  in  chewing.  The  animal  to 
be  studied  is  subjected  to  a  surgical  operation,  and  a  tube  inserted 
into  its  windpipe,  so  that  while  air  may  be  inspired  freely,  the 
expired  air  passes  through  a  rubber  tube  into  a  suitable  vessel  for 
collection.  The  expired  air  is  measured,  and  the  quantity  of  car- 
bon dioxide  and  oxygen  in  it  determined.  The  quantity  of  nitro- 
gen eliminated  in  the  urine  is  also  determined,  and  shows  how 
much  proteids  have  been  oxidized.  When  fats  are  burned,  for 
every  i  cc.  of  oxygen  which  disappears,  0.707  cc.  carbon  dioxide 
is  formed.  With  carbohydrates,  I  cc.  oxygen  is  replaced  by  i 
cc.  carbon  dioxide.  Hence  the  ratio  of  carbon  dioxide  to  oxygen 
(corrected  for  proteids  consumed)  allows  us  to  calculate  the 
relative  proportions  of  fats  and  carbohydrates  oxidized.  This 
method  cannot  be  considered  as  highly  accurate.  By  means  of 
it,  the  expenditure  of  energy  caused  by  walking  or  running  on  a 
smooth  slope,  going  up-hill,  drawing  a  load,  etc.,  have  been 
studied. 

1  Hagemann,  Exp.  Sta.  Record  10,  p.  813. 


FEEDING   WORK   ANIMALS  AND  GROWING  ANIMALS  455 

Energy  for  Work. — Work  is  measured  in  meter-kilograms,  or 
foot-pounds.  A  meter-kilogram  is  one  kilogram  raised  to  the 
height  of  one  meter.  Exact  experiments  have  shown  that  one 
large  calorie,  if  completely  transformed  into  kinetic  energy,  can 
perform  425  meter-kilograms  work.  Experiments  have  shown 
that  an  animal  can  utilize  for  work  about  one-third  of 
the  available  energy  in  the  food.  In  ten  experiments  on 
a  man  climbing  stairs,  the  percentage  was  33.1  per  cent., 
and  in  eighteen  experiments  on  a  horse,  it  was  29  to 
38  per  cent.  It  is  estimated  by  Kellner  that,  after  allowing  for 
all  losses,  I  gram  of  pure  protein  digested  will  yield  656  meter- 
kilograms  work,  i  gram  of  fat  1,214,  and  I  gram  of  carbohydrate, 
533.  The  rate  of  work,  and  the  kind,  both  affect  the  consump- 
tion of  nutrients,  also  the  shape  of  the  animal  as  related  to  the 
kind  of  work  done.  Being  accustomed  to  a  particular  kind  of 
work  also  decreases  the  oxidation  of  nutrients.  It  is  said  that  a 
man  working  a  treadmill  oxidized  25  per  cent,  less  nutrients  after 
56  days  work,  though  doing  the  same  quantity  of  work  per  day. 
According  to  the  structure  of  the  working  animal,  the  develop- 
ment of  its  muscles,  and  the  position  of  the  extremeties  doing 
the  work,  the  portion  of  the  energy  which  appears  in  the  work 
varies.  For  moving  their  own  bodies,  Zuntz  found  a  variation 
of  0.284  to  0.441  calories  per  i  kilogram  weight  and  I  meter  dis- 
tance with  different  animals.  Fatigue  increases  consumption  of 
energy. 

Rations  for  Working  Animals. — Animals  when  at  work  require 
little  more  proteids  than  when  not  at  work;  a  nutritive  ratio  of 
i :  7  is  sufficient. 

Horses  will  work  off  nutrients  fed  in  excess  of  the  maintenance 
ration  by  increased  movements  in  the  stall,  so  that  it  is  not 
possible  to  assume  that  the  maintenance  ration  is  secured  when 
an  equilibrium  between  income  and  outgo  is  secured. 

Standards  for  Work  Animals. — Two  methods  are  used  for 
studying  the  needs  of  working  animals.  One  is  to  determine  the 
maximum  amount  of  work  which  can  be  secured  with  a  given 
ration  without  loss  of  condition.  The  other  method  consists  in 


456 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


starting  with  an  insufficient  ration,  and  gradually  increasing  it 
until  it  is  sufficient  to  maintain  the  animal  under  the  required 
conditions.  Both  these  methods  have  been  used  to  a  consider- 
able extent  for  studying  the  rations  for  working  horses. 

The   following  are  standards   for   working   animals,   per   day 
and  1,000  pounds  live  weight: 


Total 
weight  dry 
matter 

Proteids 

Productive 
value 

Nutritive 
ratio 

TQ    y-j 

Pounds 

Pounds 

ft   0 

10   ^3 

2T     ift 

•3 

6.9 

ft   a 

2\    28 

•4 

3Q 

b.9 

A   ^ 

.5 

22    28 

•9 

1.4 
I  8 

*••* 

•0 

6  o 

*o   6^ 

•  * 

A  working  animal  can  utilize  somewhat  more  fat  than  a  fatten- 
ing animal. 

Feeding  Horses.1 — In  some  large  horse  establishments  only 
oat  or  wheat  straw  are  used,  as  fewer  cases  of  colic  occur  than 
when  hay  is  used.  Oats,  barley,  and  corn  are  used  for  con- 
centrates, oats  being  preferred  in  northern  climates  and  corn  in 
southern.  Corn  appears  to  be  equally  as  good  as  oats.  Care 
should  be  taken  that  the  food  is  not  musty  or  damaged,  and  horses 
should  be  allowed  2  to  2^/2  hours  for  eating  and  rest. 

Growing  Animals. — Growth  is  the  normal  condition  of  a  young 
animal.  Equilibrium  between  income  and  outgo  would  be  an 
abnormal  condition,  if  it  could  be  secured. 

With  proper  food,  young  animals  gain  in  weight  much  more 
rapidly  than  mature  animals  with  the  heaviest  fattening  ration. 
The  animals  do  not  have  smaller  maintenance  requirements,  but 
they  eat  more  in  proportion  to  weight,  and  are  able  to  store  a 
greater  excess  over  their  maintenance  requirements,  than  grown 
1  See  Bulletin  125,  Office  Exp.  Sta.,  U.  S.  Dept.  Agr. 


FKKDING   WORK    ANIMALS   AND   GROWING   ANIMALS 


457 


animals.  A  calf  two  to  three  weeks  old  has  been  known  to  re- 
tain 73  per  cent,  of  the  proteids  consumed.  As  the  animal  grows 
older,  the  percentage  of  the  food  retained  in  the  body  decreases. 
The  proportion  of  food  eaten  to  live  weight  also  decreases;  thus, 
a  larger  proportion  of  the  food  must  be  used  for  maintenance. 

The  following  experiments  of  Weiske1  were  begun  with  lambs 
four  months  old,  and  carried  out  in  7  periods  of  i^  months  each. 
The  nutritive  ratio  was  1 : 4.6  at  first  and  later,  when  about  15 
months  old,  was  i :  6.3. 

PER  50  KILOGRAMS  LIVE  WEIGHT. 


F 

?d 

Daily  gain 

Period 

Dry 
matter 

Protein 

Live 
weight 

Nitrogen 

Lime 

I    

Grams 
I   IOI 

Grams 
1  88 

Grams 
-161 

6  75 

.20 

H    

I  O71 

161 

ouo 

27T 

u-  /o 

c   TA 

37<S 

HI    

QI  7 

luo 

1  1Q 

2O6 

0-1<J 

1  71 

./u 
i  6^ 

iv  

V1  / 

QOI 

J07 

T-J« 

1  r  7 

6"  I  *• 
417 

«5-°D 

v 

SOQ 

1O° 

X6 

-1  / 

VI 

ouy 
762 

i  ly 

T08 

ftl 

.00 

2.50 
->  fi-j 

VIII 

/°^ 

0,S 

°3 

Qr 

•94 

2.03 

IX    • 

/«5o 

y° 
61 

°O 

•77 

T   8/1 

o/* 

•57 

The  quantity  of  food  per  50  kg.  weight  consumed,  decreases 
with  the  age  of  the  animal,  and  the  gain  in  weight  decreases  much 
more  rapidly.  Thus,  the  food  eaten  in  the  8th  period  is  7/11  of 
that  in  the  first,  while  the  gain  is  only  ^. 

The  increase  in  weight  of  young  animals  is  largely  flesh,  body 
organs,  and  bones.  They  thus  require  considerable  protein. 
Young  animals  also  require  more  mineral  matter  than  older  ones, 
to  build  up  the  bones.  Lime  and  phosphoric  acid  especially  are 
required.  The  preceding  table  shows  the  decreased  retention  of 
lime  with  age  of  the  animal. 

The  following  data  compiled  by  Henry  from  the  results  of  a 
number  of  feeding  experiments  with  pigs  at  various  Experiment 
Stations,  shows  the  increase  in  the  quantity  of  food  required  for 
a  pound  of  gain  as  the  animal  grows  older : 
1  Landw.  Jahrbucher,  1880,  p.  205. 
30 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Feed  eaten  per 

Weight  100  pounds  gain 

pounds  pounds 

15-50  293 

50-100  400 

100-150 437 

150-200  482 

200-250  498 

250-300 511 

300-350  535 

Mineral  Matter. — Growing  animals  retain  from  40  to  60  per 
cent,  of  the  lime  and  phosphoric  acid  in  the  food.  As  the  skeleton 
of  a  calf  a  year  old  contains  on  an  average  17  pounds  lime  and  15 
pounds  phosphoric  acid,  the  animal  must  take  up  21  grams  lime 
and  19  grams  phosphoric  acid  per  day,  and  the  food  should  con- 
tain 40  to  60  grams  each  of  these  to  meet  the  requirements.  The 
body  of  a  pig  contains  about  1.15  per  cent,  lime  and  i.io  per  cent, 
phosphoric  acid,  which  would  be  equivalent  to  a  daily  increase  of 
3.8  grams  lime  and  3.7  grams  phosphoric  acid  for  a  pig  a  year  old 
weighing  250  pounds.  As  about  3  grams  must  be  present  in  the 
food  for  i  gram  stored  up,  the  animal  will  need  12  grams  per 
day  each  of  lime  and  of  phosphoric  acid.  It  is  important  to  pay 
attention  to  the  mineral  matter  in  the  food  of  growing  animals. 

Feeding  Young  Animals. — Animals  intended  for  fattening 
should  be  fed  more  liberally  than  those  that  are  to  be  used  for 
milk  or  work.  But  with  all  animals  the  natural  development 
should  proceed  normally.  It  is  a  serious  mistake  to  assume  that 
improper  feeding  when  young  can  be  counteracted  by  liberal 
feeding  afterwards.  Young  animals  fed  with  a  deficiency  of 
proteids  yield  a  carcass  of  poor  quality  overcharged  with  fat. 

The  extreme  sensitiveness  of  young  animals  requires  care  in 
avoiding  all  injurious  influences,  in  food,  as  well  as  in  care  and 
protection.  Food  should  be  supplied  often  on  account  of  the 
limited  capacity  of  the  animal.  Regular  feeding,  clean  vessels 
for  eating  and  drinking,  good  care  of  the  skin,  a  well  ventilated 
stall,  and  clean,  dry  bedding  are  requisites  to  satisfactory  growth. 
Drafts,  cold,  and  wet,  which  affect  young  animals  much  more  than 
old  ones,  are  often  very  injurious.  Sufficient  exercise  is  neces- 


FEEDING   WORK   ANIMALS  AND  GROWING  ANIMALS  459 

sary  for  the  full  development  of  bones  and  muscles,  and  increases 
the  resistance  to  adverse  influences  of  weather  and  disease. 

Calves. — Calves  should  be  allowed  mother's  milk  for  the  first 
few  days.  Calves  intended  to  be  used  as  milch  cows  should  receive 
daily  1/7  to  1/8  of  their  live  weight  of  full  milk,  for  at  least 
three  weeks.  Animals  to  be  used  for  fattening  should  receive 
daily  1/5  to  1/6  of  their  weight  of  milk  for  about  six  weeks. 
Fresh  milk,  while  still  warm,  is  best.  Ten  liters  milk  or  1.2  kilo- 
grams solids  produce  about  I  kilogram  live  weight  increase.  The 
increase  is,  of  course,  proportional  to  the  excess  over  the  main- 
tenance requirements  and  not  to  the  live  weight. 

Other  food  should  be  introduced  gradually.  Skim  milk  may 
replace  the  full  milk  gradually,  replacing  the  fat  lost  in  skimming 
by  a  paste  made  of  linseed  or  oat  meal,  25  to  30  grams,  to  y2  liter 
of  milk.  Later  linseed  cake,  bran,  etc.,  may  be  used.  Sour  milk 
should  be  introduced  gradually. 

Calves  have  only  one  stomach  and  can  utilize  only  easily  diges- 
tible food.  As  they  grow  older,  other  stomachs  develop  and  they 
can  then  use  hay,  etc.  The  animal  gradually  becomes  accustomed 
to  hay.  At  the  end  of  the  third  month,  beets,  straw,  softened 
oats,  barley  or  pea  meal,  oil  meal,  malt  germs,  etc.,  may  be  fed. 

When  milk  alone  is  fed,  an  addition  of  about  15  grams  of  pre- 
cipitated chalk  per  day  has  been  found  beneficial.  There  is  sel- 
dom a  deficiency  of  phosphoric  acid,  but  if  straw  and  much  grain 
is  fed,  there  may  not  be  enough  lime  in  the  food. 

Lambs. — Lambs  are  usually  weaned  from  3  to  4  weeks  after 
birth.  Good  meadow  hay,  and  soaked  oats,  are  fed  and  not  too 
cold  water.  They  should  be  allowed  to  suck  often,  at  first. 
Sudden  changes  from  stall  to  pasture  are  injurious.  Lambs  thrive 
on  pasture.  They  require  stronger  food  than  calves. 

Swine. — Pigs  suck  6  to  8  weeks,  but  when  2  to  3  weeks  old 
they  begin  to  eat.  They  may  be  given  unground  barley  or  wheat 
grains  or  soaked  oats,  also  some  wood  charcoal,  hard  coal,  earth 
or  sand.  After  three  weeks,  whole  cow's  milk  heated  and  diluted 
y2  with  water,  may  be  fed.  Milk  and  grain  contain  enough  phos- 
phoric acid,  but  not  enough  lime.  It  is  well  to  add  some  pre- 


460 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


cipitated  chalk  to  the  ration,  which  should  be  increased  gradually 
from  8  to  10  grams  per  day. 

Experiments  have  shown  that  a  nutritive  ratio  of  1 : 4  is  best 
until  the  pigs  are  5  months  old,  as  it  gives  the  greatest  increase  of 
live  weight  for  the  food  consumed.  After  this  age,  the  ratio 
i :  6  is  better. 

Standards  for  Growing  Animals. — The  following  are  standards 
for  feeding  growing  animals : 

PER  DAY  AND  1,000  POUNDS  LIVE  WEIGHT. 


Pounds 
Total 


Proteids 
pounds 


Productive 

value 
pounds 


Nutritive 
ratio 


(I)  Growing  cattle,  for  milk  cows 
or  work: 


Age    2-  3  months 23 

"      3-6        "        24 

"      6-12       "        26 

"    12-18       "       26 

"    18-24      "      26 

(II)  To  be  fattened: 

Age    2-  3  months 23 

"      3-6        "        

"      6-12        "        •    26 

"    12-18        "        26 

"    18-24        "        26 

(III)  Growing  hogs,  to  be  fattened: 

Age  2-  3  months 44 

"  3-5  "  ••••  36 

"  5-6  "  32 

"  6-8  "  28 

"  9-12  "  25 

Growing  hogs,  for  breeding: 

Age  2-  3  months 44 

3-5  "  36 

11  5-  6  "  32 

"  6-8  "  28 

"  9-12*  "  25 


3-4 
2.8 

2-3 
1.8 


4-5 
3-5 
2.8 

2.2 
1-5 


6.2 

4-5 
3-5 
3-° 
2.4 

6.2 

4.o 


4-6 
3-7 
3-i 
2.6 

2-3 


4-9 
4-3 
3-6 
2.8 

2.5 


8-5 
8.0 
6.6 
6.1 
5-0 


8-5 
6.8 
5-8 
5-0 
3-9 


4-6 

4-9 
6.0 
7.0 
8.0 


4.4 
4-6 
5-5 
6-5 
7-5 


4.0 
5-0 
5-5 
6.0 

6.5 


4.0 
5-0 
5-5 
6.0 

6.5 


CHAPTER  XXIII. 


FEEDING  MILK  COWS. 

Milk  cows  are  fed  for  the  purpose  of  producing  milk  or  butter 
fat.  It  was  formerly  believed  that  milk  is  extracted  directly 
from  the  blood  of  the  cow.  But  casein  and  milk  sugar,  which  are 
constituents  of  the  milk,  cannot  be  extracted  from  blood,  because 
they  are  not  present  in  blood.  Apparently,  milk  is  elaborated 
from  the  blood  and  lymph  by  chemical  changes  within  the  cells  of 
the  udder. 

Factors  which  Influence  Milk  Production. — A  number  of  fac- 
tors influence  the  quantity  and  composition  of  the  milk. 

Breeds  of  Animals. — Milk  cows  are  divided  into  two  groups  of 
breeds,  those  giving  relatively  large  quantities  of  milk  with 
moderate  fat  content,  and  those  giving  less  milk  with  a  higher 
percentage  of  fat.  To  the  first  group  belong  the  Holsteins, 
Ayrshires,  Durhams,  etc.,  and  to  the  second,  the  Jersey  and 
Guernsey.  The  average  by  Konig  of  about  five  hundred  analyses 
of  milk  from  animals  belonging  to  these  two  groups,  is  as  follows : 


Holstein  group 

Jersey  group 

Water 

per  cent. 
87  AQ 

per  cent. 
86  87 

ProteiHs 

°/'4y 

Fat 

•4/ 

•3° 

4  86 

4-u/ 

Ash                                              •  •  • 

O  72 

O  7fS 

u.  /  ^ 

Individuality. — Individuals  of  the  same  breed  vary  decidedly  in 
the  quantity  and  composition  of  the  milk  they  give.  For  example, 
a  study  of  each  individual  in  a  herd  of  16  cows  by  Hitscher, 
showed  the  following  differences : 


Minimum 

Maximum 

270  days 
2,330.0    kg. 
74.4    kg. 
2.63 

390  days 
4,702.0    kg. 
149-3    kg. 
3.81 

462 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


The  best  cow  gave  twice  as  much  fat  and  milk  as  the  poorest. 
Some  cows  are  very  profitable,  while  others  are  fed  at  a  loss.  It 
is  important  to  test  the  individuals  of  a  herd;  the  unprofitable 
animals  should  be  sold,  and  the  feed  of  the  others  adjusted  to  the 
quantity  of  milk  produced. 

Fluctuations. — The  amount  and  composition  of  the  milk  from 
the  same  cow  may  vary  considerably  from  day  to  day.  Thus, 
Fleischmann1  found  by  daily  measurement  and  analysis,  that  the 
amount  and  composition  of  the  milk  from  the  same  cow,  varied 
as  follows : 


Total  quantity 
of  milk 

Percentage 
of  fat  in  milk 

April 
Minimum    

Kilograms 
IO  4 

2  76 

••/« 

-,    ,f. 

112 

o-4° 

3O7 

May 

8  7 

•UJ 

2   62 

Maximum   

o./ 

Average  

L6'  / 

•y*5 

1  1  .y 

.^u 

The  table  shows  a  variation  of  nearly  25  per  cent,  between  the 
maximum  and  minimum  for  April,  and  50  per  cent,  for 
May.  The  milk  from  the  other  cows  in  the  herd  varied  also,  but 
not  on  the  same  days,  showing  that  the  variations  were  not  due 
to  factors  which  influenced  the  entire  herd  alike,  but  to  individual 
differences. 

Period  of  Lactation. — The  amount  of  milk  given  decreases  with 
the  time  the  animal  has  been  giving  milk,  but  the  decrease 
varies  with  the  animal.  With  some  cows  the  decrease  is 
regular  and  gradual,  others  give  the  same  quantity  for  a  long 
time  and  then  suddenly  fall  oft".  The  following  table  from 
Fleischmann's  experiments,  shows  how  the  milk  may  decrease 
with  period  of  lactation,  and  it  also  shows  that  the  percentage  of 
fat  increases.  Cow  No.  I  behaves  somewhat  differently  from 
1  Lanclw.  Jahrbuch,  1891. 


FEEDING   MILK   COWS 


4<'>3 


<0 

5i 


I 


1 

p- 


i 


464 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


cow  No.  2,  the  decrease  with  the  period  of  lactation  taking  place 
more  regularly. 

EFFECT    OF    PERIOD    OF    LACTATION    ON    QUANTITY    AND 
COMPOSITION  OF  MILK. 


Average  quantity 
of  milk  per  day 

Average  percentage 
of  fat  in  milk 

Cow  No.  i 

Cow  No.  2 

Cow  No,  i 

Cow  No.  2 

Anril 

II.  6 
12,0 
I0.5 

8.8 
9-7 

9-i 

7-7 

6.6 
5-i 

2.2 

14.4 

J5-9 
16.6 

12.8 

12.9 

10.5 
8.5 

6.7 
5-6 

2.8 

3-0 
3-3 
3-4 

3-5 

3-6 

3-7 
3-4 

3-8 
4-3 

5-8 

3-5 

3.1 

3.0 

3-2 

3-3 

3-6 
3-4 

3-5 
3-8 

4.7 

May 

Tulv  . 

September  

October   

Age. — The  quantity  of  milk  appears  to  increase  slightly  up  to 
the  fifth  calf,  and  then  decreases  slightly.  The  fat  content  ap- 
pears to  remain  constant  for  a  long  time. 

Frequency  of  Milking. — The  more  frequently  the  cow  is 
milked,  the  greater  the  quantity  of  milk,  provided  the  milking  is 
not  done  so  often  as  to  irritate  the  udder.  This  is  shown  by  the 
following  experiment  of  Kaull  i1 


Period  of  milking 

per  milking 

Milk  per  day 

kilograms 

3-81 
2.46 
2.06 

.66 

.07 

kilograms 

76 
9.8 
12.4 
14.6 
I4.I 

As  the  udder  fills,  the  formation  of  milk  decreases.     There  is, 
1  Ber.  d.  Landw.  Inst.,  Halle,  1891. 


FEEDING   MILK   COWS 


465 


however,  a  tendency  for  the  capacity  of  the  udder  to  adjust  itself 
to  the  quantity  of  milk  produced  by  the  cow.  According  to 
Fleischmann,  from  6  to  7  per  cent,  more  fat  and  milk  are  secured 
by  three  milkings  instead  of  two.  The  number  of  milkings  should 
depend  upon  the  cost  of  the  milking  and  the  value  of  the  milk. 
Four  milkings  may  sometimes  be  justified  with  fresh  cows  of 
high  productiveness,  but  under  ordinary  conditions  not  more  than 
three,  and  often  only  two  should  be  made. 

The  shorter  the  periods  between  milking,  the  richer  the  milk 
in  fat  and  solids.  Thus,  when  three  milkings  were  made,  the 
composition  of  the  milk  was  found  to  be  as  follows  in  an  experi- 
ment by  Fleischmann : 

COMPOSITION  OF  MILK. 


Dry  matter 

Fat 

4.  oo  A    M 

per  cent. 
II  SI 

per  cent. 
2  7Q 

1  1  7Q 

3QC 

7  oo  P   M 

12  AA 

1  76 

Portion  of  the  Milking. — If  milk  is  gathered  in  fractions,  and 
subjected  to  analysis,  the  first  portions  are  found  to  be  poorer  in 
fat  and  solids  than  the  succeeding  portions.  The  following  re- 
sults were  secured  by  Boussingault  i1 

COMPOSITION  OF  SUCCESSIVE  FRACTIONS  OF  MILK. 


Weight 
of  fraction 
grams 

Peicentage 
of  dry 
matter 

Percentage 
of  fat 

628 

7 

L.  /U 

10  8s 

• 

'    "D 

6c 

1  1  61 


6  .  .  .           .         

1  T  C 

I  2  67 

•  14 

4  08 

0*0 

Not  only  are  the  strippings  very  rich  in  fat,  but  any  milk  left  in 
the  udder  decreases  the  amount  secreted.     Hence  all  the  milk 
possible  should  be  removed  at  each  milking. 
1  Ann.  Chim.,  et  Phv.,  1866 


466  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

Work. — Working  the  cow  decreases  the  quantity  of  milk  and 
fat  produced,  while  the  percentages  of  protein,  fat,  and  ash  in- 
crease. The  effect  depends  upon  the  amount  of  work  and  the 
feed  of  the  animal.  Light  work  does  not  appear  to  decrease  the 
total  production  of  dry  matter. 

Palatability  of  Food. — It  has  been  found  that  palatable  food 
increases  the  yield  of  milk.  In  experiments  in  which  two  rations 
equal  in  feeding  value  were  fed,  the  one  tasteless,  the  other  of 
well  flavored  hay,  etc.,  the  second  ration  always  gave  better  re- 
sults than  the  first. 

Other  Conditions. — The  milk  secreting  organs  are  closely  re- 
lated to  the  nervous  system.  Rough  treatment,  disturbances,  in- 
sufficient bedding,  a  cold  stall,  and  other  similar  conditions  de- 
crease the  quantity  of  milk  and  fat  produced. 

Methods  of  Investigation. — In  studying  the  effect  of  various 
conditions  upon  the  production  and  composition  of  milk,  it  is 
necessary  to  eliminate  the  influence  of  all  factors  except  the  one 
to  be  studied.  Some  of  these  factors,  such  as  the  kind  and  fre- 
quency of  milking,  may  be  eliminated  by  treating  the  animals 
alike.  Others,  such  as  individuality,  may  be  compensated  for 
by  taking  a  sufficient  number  of  animals.  Two  systems  of  experi- 
ment1 are  in  use — the  period  system,  and  the  group  system,  which 
correspond  to  the  methods  used  for  feeding  experiments  on 
fattening  animals. 

The  Period  System. — Ten  or  more  cows  are  fed  upon  a  standard 
ration  for  a  period  of  two  or  three  weeks.  Next  the  cows  are 
fed  on  the  rations  to  be  tested  during  three  periods  or  more  of 
the  same  length.  The  standard  ration  is  then  fed  for  another 
period.  In  each  period,  the  production  of  milk  and  fat  is  deter- 
mined. From  the  production  of  fat  and  milk  during  the  first  and 
the  last  periods,  we  calculate  the  quantity  which  should  be  pro- 
duced during  the  intermediate  periods,  assuming  that  a  regular 
decrease  in  production  takes  place.  We  compare  the  calculated 
production  with  that  actually  found  to  occur,  and  the  difference 
gives  the  effect  of  the  ration  we  are  testing. 

1  See  Kellner,  Ernahriing  d.  Landw.  Nutztiere,  p.  500. 


FEEDING  MII^K  cows  467 

For  example,  suppose  the  .results  with  the  standard  ration 
during  the  first  and  fifth  period  of  20  days  each,  are  as  follows : 

First  period,  average  14.27  kg.  milk  and  4.38  grams  fat  per  day 
Fifth  period,  average  13  63  kg.  milk  and  4.22  grams  fat  per  day 

Decrease    0.64  kg.  0.16  kg. 

From  the  middle  of  the  first  to  the  middle  of  the  fifth  period  is 
So  days,  or  four  periods.  The  decrease  is  thus  0.16  kg.  milk 
and  .04  grams  fat  for  each  period,  and  if  the  same  ration  were 
continued,  the  daily  production  for  each  period  should  be : 

Period  i  (found) 14.27  kg.  milk  and  4.38  grams  fat  per  day 

Period  2  (calculated)  14.11   "  "         4.34      "  " 

Period  3  13.95  "  "        4.30      " 

Period  4  13-79  "  "        4.26      " 

Period  5  (found) 13.63  "  "        4.22      "  " 

The  actual  production  with  the  ration  being  tested  during  the 
intermediate  periods  is  compared  with  the  calculated  production. 
For  example,  if  the  production  is  13.00  kg.  milk  and  4.10  grams 
fat  in  period  2,  the  ration  fed  has  decreased  the  production  i.n 
kg.  milk  and  0.24  grams  fat. 

This  method  assumes  a  regular  decrease  in  the  production  dur- 
ing the  period  of  lactation.  This  assumption  may  or  may  not  be 
true  with  one  or  two  animals,  but  with  eight  or  ten  cows,  it  is 
practically  true. 

The  difference  in  the  condition  of  the  animal  due  to  the 
previous  feeding  also  has  some  effect  upon  the  quantity  and 
quality  of  the  milk. 

Group  System. — This  corresponds  to  the  group  system  for  fat- 
tening experiments.  Each  cow  should  be  matched  in  race,  age, 
weight,  period  of  lactation,  quantity  and  composition  of  milk 
against  similar  animals  in  the  other  groups.  The  groups  are  fed 
alike  for  a  preliminary  test  period  of  30  to  60  days,  during  which 
the  yield  and  composition  of  the  milk  is  estimated.  If  any 
differences  in  the  groups  appear,  the  cows  should  be  rearranged, 
or  new  animals  brought  in,  and  another  test  made.  When  each 
group  makes  the  same  production  with  the  same  ration,  the  ex- 


468  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

periment  is  begun.  The  composition  and  quantity  of  the  milk  is 
then  determined  for  a  period  of  ten  days.  A  test  period  follows  in 
which  the  feeds  to  be  tested  are  compared.  One  method  of  pro- 
cedure is  as  follows :  Suppose  Indian  corn  and  Kaffir  corn  are 
to  be  compared.  All  groups  are  fed  roughage,  concentrates,  and 
equal  quantities  of  Indian  corn  and  Kaffir  corn  during  the  pre- 
liminary period.  At  the  beginning  of  the  test  period,  Group  A 
receives  Kaffir  corn  in  place  of  Indian  corn  and  Group  B  Indian 
corn  in  place  of  Kaffir  corn.  Group  C  receives  the  same  ration 
as  before,  containing  equal  parts  Kaffir  corn  and  Indian  corn. 
Including  the  transition  period,  the  feeding  test  lasts  I  to  2 
months,  and  every  8  to  10  days,  as  before,  the  average  milk  pro- 
duction is  determined.  In  the  last  10  days  of  the  period  the 
composition  of  the  milk  is  also  determined.  An  after  period  of 
i  to  2  months  follows,  in  which  the  food  is  the  same  as  in  the 
preliminary  feeding  period.  The  live  weight  is  also  to  be  de- 
termined on  three  successive  days  at  the  end  of  each  period  and 
in  each  sub-period.  All  factors  except  the  feed  tested  should 
remain  constant. 

Effect  of  Nutrition  on  Milk  Production. — The  composition  and 
quantity  of  milk  depends ;  first,  upon  the  capability  of  the  animal 
and  the  state  of  lactation ;  and  secondly,  upon  the  food.  The 
animal  cannot  increase  the  milk  flow  above  the  limits  of  the 
capacity  of  the  animal.  An  excess  of  feed  will  go  into  body  fat. 
A  deficiency  of  food  will  decrease  the  milk  flow,  shorten  the 
period  of  lactation,  and  may  permanently  injure  the  productive- 
ness of  the  animal.  The  food  should  be  adjusted  to  the  greatest 
quantity  of  milk  possible  to  be  produced  and  should  be  decreased 
gradually  during  the  period  of  lactation.  When  the  ration  is 
reduced  from  a  sufficient  to  an  insufficient  one,  the  milk  glands 
do  not  respond  immediately  to  the  change,  but  they  consume  more 
or  less  body  substance  for  the  production  of  milk,  and  the  condi- 
tion of  the  animal  becomes  visibly  worse.  This  fact  is  observed 
so  often  with  cows  fresh  in  milk,  that  many  believe  that  cows 
must  always  become  thinner  after  calving.  But  the  effect  of  in- 
sufficient food  soon  shows  in  a  decrease  in  the  quantity  of  milk 


FEEDING   MILK   COWS 


and  the  percentage  of  fat  and  dry  matter, 
secured  the  following  results : 


469 
For  example,  Fleischer1 


Total 
milk  produced 
per  day 

Calculated-' 
production 

Decrease 

kilograms 

kilograms 

kilograms 

M-oO 

12  7O 

*  6c 

Period  3,  insufficient  food  plus  oil  •  . 
Period  4,  insufficient  food  plus  bean 

V-uo 
8.85 

9T  C 

12.05 
1  1    ^O 

o-uo 
3.20 

2  1^ 

•AO 
IO   IO 

IO   I5* 

•*'OO 

There  was  also  a  falling  off  in  condition  of  the  animal.  The 
insufficient  food  decreased  the  milk  nearly  30  per  cent. 

Insufficient  food  also  decreases  the  ability  of  the  udder  to 
secrete  milk,  which  decrease  may  become  permanent  if  an  in- 
sufficient ration  is  fed  for  a  long  time.  The  decrease  in  produc- 
tion naturally  occurring  in  the  course  of  lactation,  is  accelerated 
by  insufficient  food,  and  diminished  by  abundant  food. 

If  we  start  with  a  very  insufficient  ration,  and  increase  it,  the 
production  of  milk  will  increase  at  first  in  proportion  to  the  addi- 
tions, and  then  the  increase  in  milk  will  be  less  for  each  equal 
increment  of  food,  until  no  effect  at  all  is  secured.  After  a  cer- 
tain amount  of  milk  is  produced,  every  increase  of  production  re- 
quires a  much  larger  amount  of  food,  increasing  quantities  of 
which  are  stored  as  body  fat.  The  highest  milk  production  is 
associated  with  an  improvement  in  condition. 

The  greater  the  productiveness  of  the  animal,  the  greater  is 
the  response  to  liberal  feeding.  For  example,  Kuhn3  determined 
the  effect  of  equal  additions  to  the  ration  of  cows  having  different 
productiveness,  to  be  as  follows : 

1  Jour.  f.  Landw.,  1871,  p.  371  ;  1872,  p.  395. 
-  Periods  of  different  length. 
3  Jour.  f.  Landw.,  1876,  p.  190. 


470 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


Cow  No.  i 

Cow  No.  2 

kilograms 

kilograms 

Increase  caused  by  addition  of  1.5  kg.  bean  meal.  . 
Increase  caused  by  addition  of  3.0  kg.  bean  meal  .  . 

11.77 
0.92 
2.40 

•4O 

0-53 

I.OI 

The  same  quantity  of  bean  meal  produced  twice  as  much  in- 
crease in  milk  with  cow  No.  i  as  with  cow  No.  2. 

Effect  of  Proteids. — The  effect  of  protein  upon  milk  flow  is 
studied  by  replacing  feeds  poor  in  proteids  by  those  richer  in 
proteids.  For  example,  Fjard  and  Friis1  replaced  barely  meal, 
which  is  poor  in  proteids,  by  oil  cake  rich  in  proteids,  in  a  number 
of  experiments  on  8  farms  and  1,152  cows,  with  the  following 
average  results: 


Group  A 

Group  B 

Group  C 

I  08 

i  18 

J  '*3 

1.38 

11«4o  Ks- 

1  I  ./U  K.g. 

Increase  of  proteids  thus  increased  the  quantity  of  milk.  It 
had,  however,  no  effect  upon  the  composition  of  the  milk.  From 
these  and  other  experiments,  it  is  concluded  that  proteids  exert 
a  great  influence  upon  the  quantity  of  milk  secreted.  The  water 
content  of  the  milk,  and  the  percentage  composition  of  the  dry 
matter  are  affected  only  when  proteids  are  fed  for  a  long  time  in 
quantities  considerably  exceeding  the  needs  of  the  animal.  In 
such  event,  the  water  content  increases  and  the  fat  decreases. 
Ammonia  salts  can  apparently  be  used  for  production  of  milk 
when  fed  in  a  ration  poor  in  nitrogen  but  rich  in  carbohydrates. 

Nitrogen-Free  Nutrients. — Since  fat  and  carbohydrates  may 
promote  flesh  production  indirectly  or  pass  into  body  fat,  it  is 
evident  that  they  may  influence  the  milk  glands  and  milk  pro- 
duction. If  the  ration  contains  enough  proteid  but  not  enough 
carbohydrates  or  fat  to  induce  the  highest  production,  the  milk 
production  would  not  reach  its  highest  limits,  but  a  part  of  the 
1  Jahresber,  f.  Agr.  Chem.,  1893,  p.  394. 


FEEDING   MILK   COWS 


471 


protein  must  replace  fat  or  carbohydrates.  The  addition  of 
carbohydrates  or  fat  should,  in  such  case,  increase  pro- 
duction. If  there  is  sufficient  proteids  and  the  nitrogen- 
free  nutrients  are  increased,  the  result  depends  upon  the 
nutrition  of  the  animal  and  the  capacity  of  the  milk 
glands,  and  also  upon  the  depression  in  digestion  of  proteids 
caused  by  the  additions.  If  the  latter  occurs  to  a  great  extent,  a 
decided  depression  in  milk  yield  will  take  place,  while  with  more 
proteids  in  the  ration,  a  less  decided  effect  will  be  produced.  With 
poorly  nourished  but  productive  animals,  the  additions  would 
cause  an  increase  in  milk  due  to  better  nutrition,  which  would 
not  appear  in  the  case  of  a  better  nourished  or  a  less  productive 
animal.  The  result  of  the  addition  would  therefore  be  different 
according  to  conditions,  and  experiments  may  give  contradictory 
results. 

Both  carbohydrates  and  fat  of  the  feed  take  part  in  the  pro- 
duction of  milk  fat.  For  example,  from  an  experiment  of  W.  H. 
Jordon,1  we  can  calculate  the  maximum  quantity  of  fat  possible 
to  be  formed  from  the  fat  fed  and  the  proteids  fed,  and  we  know 
from  analyses  the  quantity  of  fat  in  the  milk : 


Experiment  i 

Experiment  2 

Fat  fed  in  feed  

kilograms 

kilograms 

Pat  possible  from  proteids  

'•5 

7  X 

T7   8 

Total  

/•° 

17.0 

Fat  found  in  milk  

•6 

17  6 

Excess,  which  must  have  been  made  from  carbo- 
hydrates   etc  

1  /.U 

Q   i 

37-7 

°-3 

17.7 

The  increase  of  live  weight  showed  that  the  animal  did  not  lose 
weight.  After  allowing  for  all  the  fat  possible  from  protein  and 
fat  in  the  food,  there  still  remains  a  considerable  amount  of  fat 
which  could  only  come  from  carbohydrates. 

Increase  of  carbohydrates  does  not  affect  the  fat  in  milk.  Ex- 
1  Bulletin  197,  New  York  Geneva  Station. 


4/2  PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

periments  to  ascertain  the  effect  of  an  increase  in  fat  in  the  food 
on  the  quantity  of  fat  in  the  milk,  have  given  contradictory  results ; 
but  the  weight  of  the  evidence  is  to  the  effect  that  the  percentage 
of  fat  in  the  milk  is  not  modified  by  the  quantity  of  fat  in  the 
food. 

Jt  was  observed  in  Holland  that  butter  from  cows  on  pasture 
in  the  fall  decreased  in  volatile  acids.  Sjollema  found  that  beet 
heads  would  prevent  this,  and  later  found  cane  sugar  to  have  the 
same  effect.  The  pasturage  was  found  to  contain  less  carbohy- 
drates in  the  fall.  It  is  possible  that  a  part  of  the  volatile  acids 
in  butter  originate  from  the  fermentation  in  the  animal,  and  for 
this  reason,  a  smaller  amount  was  present  as  the  easily  ferment- 
able carbohydrates  in  the  food  decreased.  The  character  of  the 
fat  fed  also  has  an  effect  upon  the  composition  of  the  butter. 
Various  experiments  in  adding  oils  to  rations  have  produced  but- 
ter that  was  somewhat  affected  by  the  character  of  the  oil  fed. 

Harrington1  found  that  feeding  cottonseed  meal  made  the 
butter  much  harder,  and  decreased  the  quantity  of  volatile  acids 
in  it.  For  example,  while  normal  butter  contains  approximately 
7.0  per  cent,  fatty  acids  volatile  with  steam,  butter  made  from 
the  milk  of  cows  fed  cottonseed  contained  in  one  case  only  3.5 
per  cent,  volatile  acids. 

Standards  for  Milk  Cows. — The  amount  of  feed  to  be  fed  must 
depend  upon  the  quantity  of  milk  given  as  well  as  on  the  weight 
of  the  cow.  The  feeds  should  be  adjusted  to  the  individual 
animals,  and  not  to  the  average  of  the  herd.  The  adjustment 
may  easily  be  made  by  arranging  the  cows  in  groups  according 
to  yield  of  milk,  and  adjusting  the  ration  by  measuring  different 
quantities  of  the  concentrates  for  each  group.  The  value  of  the 
milk  as  related  to  the  cost  of  the  feed  must  determine  whether  the 
milk  production  should  be  forced  to  a  maximum  by  giving  a 
heavy  ration,  or  whether  a  somewhat  lower  ration  should  be  fed 
for  more  economical  production.  As  stated  before,  the  produc- 
tion of  the  largest  possible  amount  of  milk  requires  much  more 
food  than  the  production  of  a  somewhat  smaller  amount,  as  the 
effect  of  each  addition  of  food  on  production  diminishes  as  the 
1  Texas  Bulletin,  u. 


FEEDING    MILK   COWS 


473 


quantity  of  feed  is  increased,  and  becomes  very  small  near  the 
upper  limits  of  the  capacity  of  the  animal. 

For  the  production  of  one  pound  of  milk,  an  animal  requires 
about  0.05-0.065  pounds  proteids,  and  0.05-0.07  pounds  produc- 
tive value,  in  addition  to  maintenance  requirements.  Milk  contains 
o.i 8  per  cent,  lime  and  0.15  per  cent,  phosphoric  acid.  Only  about 
one-third  of  the  lime  and  phosphoric  acid  is  digested,  so  that  id 
pounds  of  milk  would  require  about  25  grams  each  of  lime  and 
phosphoric  acid.  To  this  must  be  added  the  maintenance  re- 
quirements of  45  grams  of  lime  and  22  grams  of  phosphoric  acid 
per  1,000  pounds.  The  requirements  for  phosphoric  acid  are 
generally  met  by  the  food,  especially  when  meadow  hay,  clovers, 
or  good  green  fodders  are  used,  but  the  requirements  for  mineral 
matter  must  not  be  entirely  left  out  of  consideration.  Precipitated 
phosphate  of  lime  may  be  used  if  the  ration  is  deficient  in  lime 
and  phosphoric  acid.  If  deficient  in  lime  alone,  precipitated 
chalk  will  supply  the  deficiency. 

The  following  are  the  amounts  of  nutrients  desirable  per  day 
and  1,000  pounds  live  weight  for  milk  cows: 


Phos- 

Yield 

Total 
weight 

Proteids 

Produc- 
tive value 

Nutritive 
ratio 

Ume 
grams 

phoric 
acid 

grams 

22-27 

•  6  8 

**   "t 

••O 

7U 

4/ 

Twenty  pounds  milk  - 

25-29 

2.O 

2.7 

:6.8 

95 

72 

Thirty  pounds  milk  •  • 

27-33 

2.8 

3-5 

:6.5 

120 

97 

Forty  pounds  milk  .  .  • 

27-34 

3-7 

4.2 

:6.5 

145 

122 

For  maintenance  only 

15-21 

0.7 

i-5 

:  10 

— 

For  each  10  Ibs.  milk  . 

0-55 

0.6 

— 

— 

— 

The  figures  given  above  for  the  productive  value  are  for  pro- 
duction at  the  maximum  capacity  of  the  animal.  For  a  slightly 
smaller  production,  the  productive  value  may  be  reduced  5  to  10 
per  cent.  The  Wisconsin  Experiment  Station1  recommends  as 
a  good  working  rule,  to  feed  as  many  pounds  of  concentrates 
(grain  feeds)  each  day,  as  the  cow  produces  pounds  of  butter  fat 
per  week,  in  addition  to  as  much  roughage  as  she  will  eat  up 
clean. 

1  Bulletin  No.  200 ;  Research  Bulletin  No.  13. 
3* 


CHAPTER  XXIV. 


FEEDING  STANDARDS  AND  FEEDING. 

Feeding  standards,  as  have  previously  been  given,  are  placed  in 
the  form  of  tables  showing  the  quantity  of  the  different  nutrients 
which  should  be  fed  to  animals  of  the  .various  kinds. 

Basis  of  the  Standards. — The  standards  are  based,  first,  upon 
exact  experiments  to  ascertain  the  needs  of  animals,  such  as  de- 
scribed in  the  preceding  pages ;  secondly,  on  feeding  experiments 
with  various  rations,  carried  on  in  large  number  and  in  various 
parts  of  the  world,  in  which  the  effects  of  the  rations  were  deter- 
mined; thirdly,  on  the  experience  of  practical  feeders  of  large 
numbers  of  animals. 

What  the  Standards  Represent. — The  standards  represent  the 
rations  which  should,  as  a  rule,  give  the  best  results.  The  in- 
dividuality of  the  animal  will  be  considered  by  the  wise  feeder, 
and  the  ration  adapted  as  may  be  necessary.  The  standards  must 
in  no  case  be  regarded  as  iron-clad  rules,  but  are  merely  intended 
to  enable  a  feeder  to  start  with  a  well-based,  average  ration.  He 
should  then  modify  or  adapt  the  ration  to  suit  the  requirements 
of  his  animals. 

Suitability  of  Feed. — Suitability  of  the  feed  must  be  consid- 
ered. Some  animals  are  able  to  take  only  small  quantities  of  a 
particular  feeding-stuff,  or  none  at  all.  The  palatibility  of  the 
food  is  also  to  be  considered.  A  mixture  of  a  number  of  foods 
diminishes  danger  from  any  suspicious  food,  and  distributes  the 
work  of  digestion  over  the  different  digestive  organs.  Every 
change  in  food  should  be  gradual,  covering  a  period  of  4  to  7 
days,  even  when  the  change  consists  only  in  a  change  in  quantity. 

The  Nutritive  Ratio. — The  nutritive  ratio  is  the  ratio  of  digest- 
ible protein  to  digestible  non-protein.  We  add  together  the 
digestible  crude  fiber,  the  digestible  nitrogen-free  extract,  and  the 
digestible  ether  extract  multiplied  by  2.25,  and  divide  the  sum  by 
the  digestible  protein.  The  following  is  an  example : 


FEEDING  STANDARDS  AND  FEEDING  475 

Digestible  Nitrogen-free  extract 9.6 

Digestible  crude  fiber 14.7 

Digestible  ether  extract  22.4  X  2.25 50.4 

Total 74. 7 

Digestible  protein 14.4 

Nutritive  ratio I   :  5.2 

The  nutritive  ratio  is  to  be  taken  chiefly  as  an  aid  in  calculating 
the  ration.  The  productive  value  of  the  ration,  and  its  content 
of  proteids,  are  the  important  factors  to  be  considered.  The 
nutritive  ratio  should  not  exceed  1 :  10  for  ruminants  or  1 :  12  for 
hogs,  but  rations  containing  more  protein  can  be  used,  if  desired. 
Protein  is  usually  the  expensive  portion  of  a  ration,  but  there  are 
localities  in  which  feeds  rich  in  protein  are  as  cheap  as  other 
concentrates,  or  cheaper.  Such  feeds  may  then  be  used  in 
moderate  quantity  for  fattening  or  other  productive  purposes. 
The  nutritive  ratio  is  given  in  the  table  mainly  to  aid  in  calculat- 
ing the  ration  which  contains  a  desired  productive  value 
associated  with  a  certain  quantity  of  protein.  With  some  feeds 
it  may  be  that  the  quantity  of  protein  so  calculated  may  exceed 
the  requirements  of  the  standards,  but  if  so,  adjustment  may  be 
made  by  the  methods  to  be  pointed  out. 

Proteids. — The  amides  and  amido  compounds  have  little  value 
for  the  production  or  repair  of  flesh.  They  may  aid  in  the  diges- 
tion of  food  when  there  is  a  large  quantity  of  non-protein  com- 
pared with  the  quantity  of  protein  present,  but  otherwise  they 
apparently  have  little  value.  Hence  it  is  better  to  base  the  ration 
on  its  proteid  content,  and  not  on  the  protein.  The  standards 
which  we  have  given  are  based  upon  digestible  proteids  and  not 
on  protein. 

Pat. — The  quantity  of  fat  is  not  material,  provided  that  it  does 
not  exceed  one  pound  per  thousand  live  weight  of  the  animal. 
If  it  exceeds  this  limit,  it  may  derange  the  digestion  of  the 
animal. 

Ash. — As  a  rule  the  food  contains  a  sufficient  quantity  of  ash 
for  the  body,  but  the  ash  requires  consideration  in  the  case  of 
young  animals.  Young  animals  require  lime  and  phosphoric 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 

acid  for  the  purpose  of  forming  bones.  A  deficiency  of  either 
of  these  is  liable  to  cause  injury,  or  disease.  In  certain  localities, 
the  food  is  deficient  in  ash.  Deficiency  in  lime  alone  is  corrected 
by  the  use  of  precipitated  chalk;  in  phosphoric  acid,  by  the  use 
of  precipitated  or  ground  phosphate  of  lime. 

Exact  Calculation  of  a  Ration. — Before  beginning  to  calculate 
a  ration,  it  is  necessary  to  decide  on  the  ration  desired,  the  feeds 
available,  and  their  probable  composition.  In  calculating  the 
ration  we  must  consider: 

(1)  The  desired  productive  value. 

(2)  The  desired  bulk. 

(3)  The  desired  proteid  content. 

All  these  may  vary  somewhat,  especially  the  bulk  and  the 
proteids. 

We  will  term  the  method  of  calculation  given  below,  the  method 
of  substitution.  It  is  best  illustrated  by  an  example.  Suppose 
we  desire  a  ration  with  a  bulk  of  about  28  pounds,  proteids  2.0 
pounds,  and  productive  value  of  2.8  pounds,  and  wish  to  use 
corn  chops,  cottonseed  meal,  and  cottonseed  hulls,  having  the 
composition  given  in  the  table  at  the  end  of  this  chapter.  As 
these  feeds  all  contain  about  ten  per  cent,  water,  for  which  allow- 
ance has  been  made  in  considering  the  total  bulk  to  be  fed,  it  is 
not  necessary  to  calculate  to  dry  matter. 

First,  let  us  assume  that  the  28  pounds  fed  is  entirely  cotton- 
seed hulls.  This  quantity  of  cottonseed  hulls  has  a  productive 
value  of  0.84  pounds,  and  the  value  desired  is  2.80  pounds,  leaving 
a  deficiency  of  1.96  pounds.  If  now  we  replace  cottonseed  hulls 
having  a  productive  value  of  0.03  a  pound  by  corn  chops,  having  a 
productive  value  of  0.206,  for  every  pound  of  cottonseed  hulls  re- 
placed, we  gain  0.206-0.03  — -  0.176  pounds  productive  value. 
Dividing  1.96  by  0.176  we  have  n.i  pounds  corn  chops,  which 
should  replace  an  equal  amount  of  cottonseed  hulls. 

Cottonseed  hulls  17.9  pounds  and  corn  chops  n.i  pounds  con- 
tain 0.86  pounds  proteids,  while  2.0  pounds  is  desired,  a  de- 
ficiency of  1.14  pounds  proteids.  Since  cottonseed  meal  has 


FEEDING   STANDARDS  AND  FEEDING  477 

nearly  the  same  productive  value  as  corn  chops,  it  can  replace 
corn  chops  without  materially  altering  the  productive  value  of 
the  ration.  If  one  pound  average  cottonseed  meal  containing  0.352 
pounds  digestible  protein  replace  one  pound  corn  chops  contain- 
ing 0.065  pounds  digestible  protein,  the  digestible  protein  increases 
0.352-0.065  =  0.287  pounds,  so  that  to  increase  the  ration  1.14 
pounds,  we  require  1.14  divided  by  0.287  —  4.0  pounds  cottonseed 
meal  in  place  of  an  equal  quantity  of  corn  chops.  The  ration 
would  then  consist  of  17.9  pounds  cottonseed  hulls,  7.1  pounds 
corn  chops,  and  4  pounds  cottonseed  meal.  The  substitution  of 
i  pound  cottonseed  meal  for  I  pound  corn  chops  decreases  the 
productive  value  0.206-0.195  =  o.oi,  or  0.04  pounds  for  the  4 
pounds  substituted;  and  this  can  be  adjusted  by  adding  0.25 
pounds  corn  chops,  making  a  total  of  7.35  pounds  corn  chops  in 
the  ration.  This  finally  gives  the  ration  desired. 

The  method  of  calculation  here  given  is  as  follows : 

(1)  Assume  the  bulk  desired  is  composed  of  the  roughage  to 
be  used  and  calculate  its  productive  value. 

(2)  Calculate  the  quantity  of  concentrate  which  would  give 
the  desired  productive  value  if  it  replaced  a  portion  of  the  rough- 
age. 

(3)  Calculate  the  proteids  in  the  mixture  having  the  composi- 
tion ascertained  above,  and  then  calculate  the  quantity  of  a  con- 
centrate, rich  in  proteids,  which  must  replace  a  portion  of  the 
other  concentrate  in  order  to  give  the  desired  quantity  of  pro- 
teids.    The   calculation   is   easier   if   the  two  concentrates   have 
nearly  the  same  productive  value. 

(4)  Adjust  the  ration  by  increasing  or  decreasing  the  quantity 
of  one  of  the  concentrates  slightly,  so  that  the  change  in  the 
productive   value    caused    by   the    second    concentrate    may   be 
allowed  for. 

Improving  a  Ration. — Suppose  a  horse  weighing  1,000  pounds 
at  hard  work,  plowing  for  example,  is  receiving  7  pounds  corn,  6 
pounds  wheat  bran,  and  12  pounds  timothy  hay.  How  does  this 
ration  compare  with  the  standard  and  how  can  it  be  improved? 


478 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


First,  calculate  the  digestible  proteids  and  productive  value  of 
the  ration. 


Digestible  proteids 

Productive  value 

Corn   •  •         

7  X  °  °68  —  o  48 

7\S  Q  206  —  I  AA 

Wheat  bran  .  .          

6  X  O   12      —  O  72 

6  X  O  12     —  O  72 

Timothy  hay  »•  • 

12  X  O  O2I   —  O  2^ 

12  X  o  078  —  o  94 

Total 

7   TO 

Standard                                   .... 

•O                             1-4o 

J.J.V 

7    8 

O'° 

The  ration  is  too  low  in  proteids  and  in  productive  value.  Pro- 
ductive value  may  be  increased  by  substituting  corn  for  timothy 
hay.  One  pound  corn  substituted  increases  the  productive  value 
0.206-0.078  =  0.128;  so  to  gain  the  0.7  pound  desired  would  take 
5.5  pounds  corn  chops.  Each  pound  of  corn  chops  substituted 
would  increase  the  proteids  in  the  ration  0.068-0.021  :  -  0.047 
pounds,  or  5.5  pounds  would  increase  it  0.26  pound.  This  would 
increase  the  total  proteids  to  1.71,  but  would  still  leave  a  de- 
ficiency of  0.29  pounds  proteids.  If  we  replace  corn  by  cotton- 
seed meal  to  supply  this  protein,  we  require  0.29  -4-  (0.352-0.068) 
=  i.o  pound  cottonseed  meal. 

The  calculated  ration  would  then  be  as  follows: 

Pounds 

Corn 7  -f  5.5  —  i.o  =  11.5 

Wheat  bran =    6.0 

Timothy  hay 12  —  5.5=    6-5 

Cottonseed  meal =    i.o 


Total 


25.0 


Reducing  the  Cost  of  a  Ration. — The  commercial  prices  of 
feeding-stuffs  are  often  not  in  proportion  to  their  feeding  values, 
and  rations  may  often  be  modified  so  as  to  reduce  the  cost  of  the 
ration.  There  are  four  things  to  be  considered  in  reducing  the 
cost  of  a  ration:  (i)  the  suitability  of  the  feed  to  the  animal;  (2) 
the  cost  of  the  productive  value;  (3)  the  cost  of  the  digestible 
proteids  per  pound;  (4)  the  cost  of  the  bulk  or  volume  of  the 
feed. 


FEEDING  STANDARDS  AND  FEEDING 


479 


The  three  last  factors  can  be  calculated  from  the  known  selling 
price,  and  the  proteid  content  and  productive  value  of  the  feeds. 
The  bulk  of  the  feed  is  of  course  measured  by  the  total  amount 
of  dry  matter.  It  often  happens  that  hays  cost  more  per  unit  of 
feeding  value  than  concentrated  feeds.  In  such  cases,  the  cheaper 
bulky  feeds  should  be  used,  and  the  difference  in  nutritive  value 
compensated  for  by  increasing  the  concentrates.  The  following 
table  shows  the  relative  cost  of  nutrients  on  the  Texas  market 
in  1910-11 : 

RELATIVE  COST  OF  NUTRIENTS. 


Selling:  price 
per  ton 

Cost  of  one 
pound  digesti- 
ble protein 

Cost 
of  one  pound 
productive 
value 

$28  oo 

Cents 
r<  6 

Cents 

7  "^ 

Wheat  shorts  •          

28  oo 

5-v 

jo  7 

7  Q 

27  OO 

10  8 

112 

27  OO 

2O  7 

6  q 

oc  OO 

17  8 

6  8 

Milo  maize  chops  

25  oo 

17  8 

68 

Rice  polish  

24  oo 

I  A  A. 

c  7 

1  8  OO 

4C 

8  i 

•o 

5C 

^O-O0 
8  e;o 

70  8 

IA  I 

Alfalfa  hay  

18  «;o 

TO     T. 

II  7 

***o 

Suppose  a  feeder  who  is  using  6  pounds  wheat  bran  at  a  cost  of 
$30.00  a  ton,  can  secure  corn  at  $30.00  and  cottonseed  meal  at 
$40.00.  Would  it  pay  to  substitute?  Six  pounds  wheat  bran 
contains  0.72  pounds  proteids  and  0.72  pounds  productive  value. 
Three  and  one-half  pounds  corn  would  contain  0.72  pounds  pro- 
ductive value  and  0.241  pounds  proteids,  or  a  deficiency  of  0.48 
pounds  proteids.  Replacing  corn  by  cottonseed  meal,  0.48  -r- 
0.352  --  0.068  =1.4  pounds.  That  is,  1.4  pounds  cottonseed 
meal  and  3.5  pounds  corn  are  equivalent  to  6  pounds  wheat  bran. 
The  cost  would  be  6  x  1.5  —  9  cents  for  wheat  bran;  and  for 
the  mixture,  1.4  x  2.0  =  2.8  cents  for  the  cottonseed  meal,  and  for 
the  corn  3.5  x  1.5  =  5.25  cents,  a  total  of  8.05  cents  for  the  mix- 
ture or  a  difference  of  0.95  cents,  nearly  one-ninth  in  favor  of 


480 


PRINCIPLES  OF  AGRICULTURAL  CHEMISTRY 


the  mixture.     The  difference  in  bulk  of  the  ration  should  be  ad- 

• 

justed  when  such  substitutions  are  made,  unless  it  comes  within 
the  range  of  the  variations  allowed. 

The  preceding  illustration  shows  the  method  which  may  be 
followed  in  reducing  the  cost  of  a  ration.  In  substituting  for  pro- 
teids,  a  suitable  feed  providing  the  proteids  at  the  lowest  cost 
per  unit  should  be  used.  In  substituting  for  productive  value 
a  suitable  feed  providing  the  most  productive  value  for 
the  money  should  be  used,  and  the  same  remark  applies  to  sub- 
stituting for  bulk. 

Tables  of  Feeding  Value. — The  following  tables  show  the  feed- 
ing values  of  a  number  of  feeds. 

AVERAGE  FEEDING  VALUE  OF  FEEDS. 


Total  dry  mat- 


Digestible  pro- 


ter  in  100  Ibs.    teids  in  100  Ibs 


Productive 
value  in  icolbs. 


GRAIN  AND  SEED 

Barley 89.1 

Corn 89.  i 

Corn  and  cob  meal 84.9 

Kaffir  corn 89.9 

Oats 89.0 

Pea  meal   89.5 

Milo  maize 89.5 

Rye 88.4 

Wheat    89.5 

Cotton  seed 89. 7 

BY-PRODUCTS 

Brewers  grains,  dry 92.0 

Cottonseed  meal,  average 91.8 

Cottonseed  meal,  Texas 92.0 

Gluten  feed,  dry 91.9 

Linseed  meal,  old  process 90.8 

Linseed  meal,  new  process 90  i 

Rye  bran 88.2 

Wheat  bran 88.  i 

Wheat  shorts 87.9 

Rice  bran 90.  i 

Rice  polish 88.5 

Corn  bran 90.9 

Peanut  meal 89.3 

Cold  pressed  cottonseed  cake 90.2 

Molasses   (cane) 77.6 

Corn  cobs 89.3 

Oat  hulls 92.7 

Rice  hulls 91.0 

Wheat  chaff 85.7 

Cottonseed  hulls 88.9 


8-4 
6.8 

4-5 

7.0 

8.0 

16.8 

7i 
8.1 

8-9 
H-5 

19.0 
35-2 
39-0 

20.0 
27-5 
29-3 

ii. 4 

12.0 
13.0 
9-0 
8-3 

6-5 
42.9 
17.1 

0.7 

0-3 
0.4 
0.9 
0.6 


18.8 

20.6 

16.5 
18.3 

150 

16.6 

18.4 
18.9 
17-3 

21.2 

14.0 

19-5 
I9.I 
18.4 
18.4 

17.4 
13.2 
12. 0 
I7.6 
19.8 
20.9 

18.6 

20.2 
10.0 
13.2 

5-3 

4.5 
0.7 

6.1 
3-° 


FEEDING  STANDARDS  AND  FEEDING 


481 


AVERAGE  FEEDING  VALUE  OF  FEEDS.— (Continued.} 


Total 

dry  matter 
in  100  Ibs. 


Digestible 
proteids 
in  100  Ibs. 


Productive 
value  in 
100  Ibs. 


GREEN  FODDER  AND  SILAGE 

Alfalfa 28.2 

Red  clover 29.2 

Crimson  clover 19.1 

Corn  fodder 20.7 

Corn  silage 25.6 

Rape 14.3 

HAY  AND  COARSE  FODDER 

Alfalfa 91.6 

Clover  hay I  84.7 

Corn  forage 57.8 

Cowpea  hay 89.3 

Oat  hay 84.0 

Timothy  hay 86.8 

Oat  straw 90.8 

Rye  straw 92.9 

Wheat  straw 90  4 

Rice  straw 88.0 

Corn  shucks 87.2 

ROOTS  AND  TUBERS 

Carrots 11.4 

Mangel  wurzels 9.1 

Potatoes 2 1 .  i 

Rutabagas 1.4 

Turnips 9.4 


2.5 

2.2 

2.2 
0.4 
1.2 
2.2 

69 

5-4 

2.1 

8.6 
2.6 

2.1 
I.I 

0.6 
0.4 
i.o 
i.o 

0.4 

O.I 

0.5 
0.9 

O.2 


2.9 

3-8 

2.6 

2.9 

3-9 
2.6 


7-9 
8.1 


JO.O 

8.6 
7.8 
4-9 
4-9 
3-9 
3-4 
8.2 

1.8 
i.i 
4.2 
1.8 


INDEX 


Absorption,  152,  240. 
Acid  consumed,  187. 
Acid,  effect  on  digestion,  406. 
Acid  phosphate,  306. 
Acid  soils,  160,  162,  250. 
Acidity,  detection,  253. 
Acids,  fatty  in  feeds,  353. 
Acids  in  feeds,  376. 
Active  plant  food,   180. 

significance,  187. 
Ahesion   of   soils,    115. 
Aerobic  bacteria  286. 
Agricultural  chemistry,  2. 
Agriculture,  object,   i. 
Air,  carbon  dioxide  in,  37. 

composition,  36. 

relation  to  plant,  6. 
Amendments,  293. 
Amides,  358. 

value  in  feeding,  475. 
Ammonia  absorbed  by  leaves,  47. 

assimilation,  219. 

of  air,  46. 

production  in  soil,  215. 
Ammonification,  204,  208. 
Ammonifying  power,  210. 
Amylopsin,    394. 
Albite,  150. 
Albumins,  357. 
Alcohols,  wax,  157,  349. 
Alfalfa,  fertilizer  for,  344. 

meal,  391. 
Alkali,  black,  258,  265. 

effect  on  plants,  263. 

origin,  259. 

prevention,  267. 
Alkali,  white,  258. 
Alkali  soils,  258. 

classes,   265. 

utilization,  265. 


Alkaloids,  360. 
Alluvial  soil,  66,  96. 
Animals,  composition,  411. 

composition  of  gain,  442. 

feeding  young,  458. 

growing,  456. 
Animal   production,  3. 
Apatite,  15,  155,  184,  305. 
Appalachian  mountain  soils,  76. 
Appetizers,  434. 
Arabinose,  366. 
Argon,  46. 

Arid  climate,  50,  139. 
Arid  soils  77,  178... 
Ash,  346. 

constituents,  n. 

effect  of  soil  and  season  on,  22. 

essential,  10. 

excess  taken  up  by  plants,  24,  191. 

importance,  9. 

indifferent,  19. 

minimum  needed,  20. 

needed  by  animals,  458. 

not  created,  10. 

of  leaves,  22. 

of  plants   (table),  23. 

of  roots,  21. 

of  seeds,  21. 

of  straw,  22. 

of  tubers,  21. 

stage  of  growth  affecting,  26. 

strong  and  weak  plants,  25. 

variations,  22. 

value  in  feeding,  458,  475. 

washed  from  plants,  20. 
Asparagin,  359. 

value  for  maintenance,  438. 
Atlantic    and    Gulf    Coastal    Plain 

soils,  75. 
Atmosphere,  36. 


484 


INDEX 


Atmosphere,  soil,  51. 
Available  energy,  420. 
Availability  of  plant  food,  181. 

Bacteria,  205. 

classes,  208. 

destroyed  by  ozone,  49. 

in  air,  49. 

in  animals,  394. 

in  manure,  286. 

soil,  205. 
Bacteriods,  222. 
Bagasse,  369. 
Barium  in  plants,   n. 
Barley,  depth  of  rooting,  104. 
Basalt,  65. 
Bat  guano,  297. 
Bile,  303. 
Biotite,    151. 
Blood,  296. 
Bone  black,  304. 
Bone  meal,  304. 
Boron  in  plants,  n. 
Buckwheat,  water  culture,  12. 
Butter,  volatile  acids  of,  472. 

Cabbage,  fertilizer  for,  345. 
Calcareous  soils   (see  lime),  186. 
Calcium  cyanamid,  45,  295. 
Calcium,  essential  to  plants  13. 
Caliche,  294. 
Calorimeter,  377. 

respiration,  415. 
Calorie,  377. 
Calves,   feeding,  459. 
Cane  sugar,  368. 
Capillary  action,  140. 

moisture,  129. 
Carbohydrates,  361,  410. 

digestion  of,  395. 

effect  on  digestion,  404. 

effect  on  milk  production,  470. 

form  fat,  440. 

Carbohydrates,  used  in  work,  455. 
Carbon  balance,  413. 


•Carbon    bisulphide,    effect    on    soil, 

233. 

Carbon  circulation,  39. 
Carbon  dioxide  in  air,  36. 

in  soil,  51,  59. 

solvent  action,  39. 

sources,  37. 

test  for,  36. 

weathering  by,  57,  58. 
Carbon  of  food,  use,  416. 
Carbonate    of    lime,    effect   on    soil 
texture,  87. 

solubility,  58. 

effect  on  tilth  (see  lime),  90. 
Carnallite,  309. 
Cattle,  feeding  young,  460. 
Cells,  197. 
Cellulose,  373. 
Cereals,  fertilizing,  324. 
Chabazite,  152. 
Chlorine  for  plants,  14. 
Chlorite,  153. 
Chlorophyll,  39,  360. 
Citric  acid,  376. 

in  soil,  analysis  ,180. 
Clay,  80. 

colloidal,  88. 

effect  on  soil  texture,  87. 
Clays,  86. 
Clays,  crops  for,  92. 

physical  composition  of,  83. 
Clover,  depth  of  rooting,  104. 

fertilizer  for  344. 

Coefficient  of  digestibility,  398,  408. 
Cottonseed  meal,  297,  391. 
Colloidal  clay,  88. 
Colluvial    soil,   63. 
Concentrates,  389. 

digestion  experiments  on,  401. 

effect  on  digestion,  405. 

productive  value,  425,  480. 
Cooking,  effect  on  digestion,  407. 
Copper  in  plants,  n. 


INDEX 


485 


Corn,  depth  of  rooting,   104. 

fertilizer  for,  344. 
Cotton,  fertilizer  for,  344. 
Cottonseed,  297,  370. 
Cottonseed  hulls,  digestibility,  408. 
Cottonseed  meal,  297,  391. 
Cover  crops,  291. 
Cows,   feeding,   461. 
Crude  fiber,  346. 

digestion,  394. 

heat   value,   409.    . . 

loss  of  energy  of,  418. 

productive  value,  422. 
Crystalline  rock,  63. 
Cultivation,  147. 
Cumulose  soil,  63. 
Cutin,  374. 
Cyanamide,   45. 

Dextrose,  370. 
Denitrification,  204,  218. 
Diffusion,  197. 
Digestion,  392. 

artificial,  399- 

energy  expended  in,  417,  420. 

experiments,   398. 

influence  of  conditions  on,  402. 

losses  of  energy  in,  418. 

marsh  gas  produced  in,  417. 

measure  of  losses  of  energy  in, 
420. 

study  of,  395- 

time  of,  398. 
Diorite,  65. 
Drainage,    141. 
Drain  gauge,  143. 
Dry  farming,  139. 
Duty  of   water,   126. 
Dynamiting  soils,  107. 

Elements,  essential  to  plants,  n. 
Energy,  available,  420. 
Energy  balance,  415. 
Energy  in  work,  455. 


Energy,  kinetic,  420. 

loss  of,  419- 

of  food,  disposition  of,  417. 

productive,  426. 

thermal,  420. 
Enzyme,  364,  392. 
Essential  oils,  377. 
Essential  elements,  13,  27. 
.Ether  extract,  346,  348. 

composition,  349. 

digestibility  of  constituents,  409. 

heat  value,  410. 

of   soils,   157. 

productive  value,  422. 
Experiment,  methods,  6. 
Experiment  stations,  I 

Fat,  composition,  414. 

effect  on  digestion,  404. 

effect  on  milk  production,  470. 

food  required  to  produce,  444. 

modified  by  food,  441. 

productive  value,  422. 

value  in  feeding,  475. 

value  for  maintenance,  435. 

value  for  work,  455. 
Fat   value,   427. 
Fats,  digestion,  39. 
Fats,  used  in  work,  453. 
Fattening,   practice   of,  450. 
Fattening    rations,     factors    which 

modify,  443. 
Feed  laws,  386. 
Feeds,  injurious,  387. 

mineral  constituents  of,  428. 
Feeds,   preparation,  388. 
Feeds,  productive  value,  423. 
Feed,     productive    values     (table), 
480. 

value  for  maintenance,  435. 
Feeding  experiments,  447. 

on  cows,  466. 
Feeding   for   maintenance,  439. 


486 


INDEX 


Feeding  standards,  437,  474. 

calculation  of  ration,  476. 

fattening,  448. 

Feeding  standards,  growing  animals, 
460. 

maintenance,  439. 

milk  cows,  472. 

work  animals,  455. 
Feeding  stuff,  387. 
Fehling's  solution,  364. 
Felspar,  150. 

Felspar,  decomposition,  59. 
Fermentation,   37,  364. 

in  stomach,  392. 
Fertilization,  practice,  343. 

systems,  336. 
Fertilizer  control,  313. 
Fertilizers,  293. 

agricultural  value,  303,  316. 

availability,  297. 

calculating  formulas,  320. 

effect  on  transpiration,  121. 

experiments,  325. 

fixation  of,  342. 

guarantee,  313. 

home  mixing,  318. 

mixed,  312. 

phosphates,  303. 

purchase,  317. 

quantity  used,  339. 

use,  322. 

valuation,   314. 

wet  mixed,  312. 
Field  experiments,  245,  332. 
Filler,  312. 
Fish,  dried,  297. 
Fixation,  240. 

by  zeolites,   152. 
Flesh,  composition,  412. 
Flood  plain,  67. 
Fluorine,  plant  stimulant,  29. 
Fructose,  367. 
Furfural,  365. 


Galactose,  367. 

Gastric  juice,  392. 

Germination',  109,  379. 

Gibbsite,  156. 

Glaciers,  56. 

Glacial  soils,  68,  76,  97. 

Glassy  rock,  83. 

Glauconite,  153. 

Globulins,  357. 

Glucose,  366. 

Glutelins,  357. 

Glycerides,  352. 

Glycogen,  372. 

Granite,  65. 

Green  sand  marl,  153. 

Grinding,  effect  on  digestion,  407. 

Gums,  373. 

Gypsum,  255. 

Hair,  fertilizer,  297. 
Hard  pan,  106. 
Hay,  383. 

curing,  384. 
Hemicellulose,  374. 
Hentrioontane,   157. 
Hexose,  365,  366. 
Hippuric  acid,  418. 
Hogs,  fattening,  452. 
Hogs,  feeding  growing,  460. 
Hornblende,  151. 
Horse,  digestive  power,  402. 

feeding  standard,  456. 
Humic  acid,  362. 
Humid  climate,  50. 
Humus,  162. 

estimation,  164. 

formation,  278. 

importance,  165. 

of  peat  and  swamps,  164. 

theory  of  plant  nutrition,  9. 

value,  232. 
Hydration,  57. 
Hydrocarbons,  355. 


INDEX 


487 


Hydrogen   peroxide,   48. 
Hygroscopic  water,  127. 

Igneous  rocks,  63. 

Iodine  in  plants,  63. 

Inulin,  372. 

Ions,   198. 

Irrigation,   261. 

Irrigation  water,  quality,  269. 

Iron,   essential   to   plants,   13. 

in  soils,  178. 

minerals,    154. 

plant  stimulant,  29. 

Kainit,  310. 
Kaolin,    153. 
Kaolinite,  153. 
Kinetic  energy,  420,  427. 

Lactation,  462. 
Lactic  acid,  376,  393. 

productive  value  422. 
Lactose,  369. 
Lake  deposits,  74. 
Lambs,   feeding,  459. 
Law  of  minimum,  30,  32. 
Lead  in  plants,  n. 
Leather,  297. 
Leaves,  ash  of,  21. 
Lecithin,  354,,  431. 
Legumes  assimilate  nitrogen,  221. 

inoculation,  227. 
Leucin,  359. 
Light,  effect  on  plants,  5,  39,  40. 

control  of,  42. 
Lignin,  374. 
Lime,  1 1 6. 

application,  255. 

and  acidity,  250. 

burning,  37. 

carbonate,    154. 

effect   on   crops,   252. 

effect  on  digestion  406. 

effect  on  nitrogen  assimilation,  224. 

experiments  with,  237. 


Lime,  effects,  254. 

in  feeds,  428. 

liberates  potash,  256. 

loss  by  weathering,  61,  273. 

need  of  animals  for,  452. 

per  cent,  in  soils,  175. 

ratio  to  magnesia,  28. 
Limestone,  73,  256. 

solubility  58. 

Limestone  valley  soils,  76. 
Linseed  meal,  297. 
Lipase,  393. 
Litter,  283. 
Loams,  86. 

crops  for,  92. 
Loess,  70,  71. 
Loess  soils,  76. 

Magnesium,  essential  to  plants,  13. 

Maintenance  ration,  435. 

Malic  acid,  376. 

Malt,  372. 

Maltose,  370. 

Maganese,  plant  stimulant,  29. 

Mannose,  367. 

Manure,  218,  280. 

application,  289. 

fermentation,    286. 

green,  290. 

horse,  282. 

losses  of,  284. 

poultry,   282. 

saving,  287. 

sheep,  282. 
Marsh  gas,  394. 
Marsh  gas  in  air,  49. 

estimation,  414, 

from  animals,  417. 
Men,  digestion  experiment  on,  399. 
Metabolic  nitrogen,  36. 
Metabolic  products,  395: 
Metamorphic  rock,  63. 
Mica,  151. 


488 


INDEX 


Milk,  composition,  461. 

effect  of  conditions  on,  462. 

effect     of     feed     on     production^ 

methods,  466. 
Milk  fat,  production,  471. 
Milk  production,  effect  of  nutrition 

on,  468. 

Milk   sugar,   369. 
Milking,  frequency,  464. 
Minerals,  149. 
Mineral  matter,  needed  by  animals, 

458. 
Mineral  theory  of  plant  nutrition, 

9- 

Moraine,  69. 
Mucic  acid,  367. 
Muck  soils,  74. 
Muds,  73. 

Muriate  of  potash,  310. 
Muscovite,  151. 

Nitrate  of  soda,  293. 

use,  338. 
Nitrates,  accumulation,  218. 

electrical  production  45. 

production  in  soil,  215. 
Nitric  acid  of  air,  47. 
Nitrifying  power,  214. 
Nitrifying  capacity,  214. 
Nitrogen,     accumulation     in     soils, 

54- 
Nitrogen,   assimilation  by  bacteria, 

45- 

assimilation  by  legumes,  211. 
Nitrogen,   availability,   300. 
Nitrogen  balance,  412. 
Nitrogen,  circulation,  45. 

combination  of  free,  45. 

essential  to  plants,  13. 

gains  by  soil,  275. 

in  rain,  48. 

in  rocks,  54. 

loss  from  soils,  273,  277. 

of  air,  44. 


Nitrogen  of  food,  use,  417. 

of  soil  atmosphere,  51. 

relation  to  pot  experiments,    193. 

fixation,   204,   220. 

fixing  power,  220. 
Nitrobacter,  212. 
Nitrification,  204,  210. 
Nitrification,  conditions,  214. 

study  of,  213. 
Nitrogen-free  extract,  346,  360. 

composition,  375. 

digestibility   of    constituents,  408. 

heat  value,  410. 

loss  of  energy  of,  418. 

productive  value,  426. 
Nitrogenous   fertilizers,  293. 
Nutrients,  productive  value,  422. 
Nutrients  used  in  work,  453. 
Nutritive  ratio,  440,  474. 

effect  on  digestion,  406. 

Oats,  fertilizer  for,  344. 

Observation  and  experience,  7. 

Oils,  351. 

Onion  fertilizer,  345. 

Organic  matter  (see  humus),  4. 

decomposition,  229. 

decreases  cohesion,   116. 

gains,  278. 

of  soil,  228. 

and  soil  temperature,  112. 
Organic  theory   of   plant  nutrition, 

9- 

Orthoclase,  150. 
Oxalic  acid,  376. 
Ox,  feeding  standard,  456. 
Oxen,  compositon  of  gain,  443. 

fattening  ration,  449. 
Oxygen,  42. 

for  germination,  42. 

weathering  action,  58. 
Oyster  shells,  256. 
Ozone,  49. 


INDEX 


489 


Pacific  coast  soils,  78. 

Palmitin,  351. 

Pancreatic  juice,   394. 

Peat  soils,  74. 

Pectins,  373. 

Pentosans,  digestibility,  408. 

in  soils,   157. 
Pentoses,  365,  374. 
Pepsin  393- 
Peptones,  357. 
Percolation,  142,  271. 
Phytin,  377. 
Piedmont  plains,  67. 

soils,  75. 
Pigs,  digestive  power,  402. 

fattening  ration,  449. 

feeding  young,  459. 
Finite,  153. 
Plants,      absorption      of      carbon 

dioxide,  36. 

Plants  and  atmosphere,  6,  30. 
Plant   constituents,    n. 
Plant  food,  active,  180. 

definition,  17. 

factors  of  availability,  181. 

and  crops,  276. 

and  soils,   172. 

minimum  requirements,  18. 

quantity    needed,    20. 

washed  out,  20. 
Plant  life,  conditions,  5. 

essentials,  9. 

products,  4. 
Plants,  light  on,  39. 
Plant  production,  3. 
Plant  stimulants  29. 
Polariscope,  363. 
Porphyry,   64. 
Plant,  ash  essential  to,  10. 

ash  of    (table),  23. 

assimilation    of    organic    matter, 
161. 
32 


Plants,  color  of  light  on,  40. 

composition  at  stages  of  growth, 
38o. 

conditions  for  life  of,  5. 

constituents,  346. 

effect    of    temperature,    ICQ. 

effect   of    space   on    development, 
105. 

essentials  for  life,  9,  30. 
Plants,  harvesting,  382. 

law  of  minimum,  30. 

ratio  essential  elements,  27. 

selection,  383. 

variable  conditions,  32. 

water  required,   119,   124. 
Plowing,  labor  of,  116. 
Phosphates,  soil,  155,  303. 
Phosphates,  availability,  308. 
Phosphoric  acid,  18. 

active,    183. 

ammonia,  soluble  166. 

available,  307. 

changes  in  soil,  241. 

fixation,  184,  234. 

in  rations,  428. 

percentages  in  soils,   174. 

needs  of  animals  for,  458. 

relation   of  active  to   pot  experi- 
ments, 189. 

reverted,  306. 

water-soluble,  306. 
Phosphoric  acid  essential  to  plants, 

13- 
Pot  expe-riments,  184,  193. 

conduct,  246. 
Potash,  active,   183. 

excess  taken  -up,   192. 

fixation,  185. 

loss  from  soils,  273. 

loss  by  weathering,  61. 

relation  of  active  to  pot  experi- 
ments,  191. 
Potash    salts,   definition,   74. 


490 


INDEX 


Potash,  sources,  308. 
Potash   of    soils,    176. 
Potassium  essential  to  plants,  13. 
Potatoes,  depth  of  rooting,   104. 
Potato  fertilizer,  345. 
Prairie  soils,  77. 
Primary  minerals,   149,   150. 
Productive  value,  427. 

calculation  of,  423. 

of  feeds,  422. 
Protamins,  357. 
Proteids,  356. 

classes,  357. 

digestion,  394. 

effect  on  milk  production,  470. 

form  fat,  440. 

value  for  maintenance,  438. 

productive  value,  422. 

value  in  feeding,  475. 
Protein,  346,  355. 

digestion  of,  405. 

used  in  work,  453. 

value  for  maintenance,  438. 

value  for  work,  455. 
Proteoses,  357. 
Ptyalin,  392. 
Putrefaction,  207. 
Pyrite,  155. 
Pyroxene,  151. 

Quartz,  150. 
Quicklime,  255. 

Raffinose,  367,  370. 

Rain,   nitrogen    in,   48.' 

Rainfall  relation  to  yield  of  crops, 

125- 
Ration,  calculation  of,  476. 

improving,  477. 

reducing  cost  of,  4/8. 

restricted,  435. 
Rennin,  393. 
Respiration  calorimeter,  415. 

chamber,  414. 


Respiratory   methods,   454. 
Rhamnose,  366. 
Rice  bran,  391. 
Rivers,  carrying  power,  66. 
River  deposits,  67. 
Rock,  crystalline,  63. 
Rocks,    final    weathering    products 
of,  60. 

glassy,  63. 

granite,  65. 

igneous,  63. 

metamorphic,  63. 
Rocks,   solution   of,   57. 

weathering  of,  54. 

stony,  64. 

Rocky  Mountain  soils,  78. 
Rothamsted,   foundation   of,    10. 
Root  absorption,  198. 
Roots,  ash  of,  21. 

acidity,  180. 

depth  of  penetration,  102. 

need  for  oxygen,  43. 

solvent  action,  200. 

root  tubercles,  212. 
Roughage,  390. 

productive  value,  425,  480. 
Ruminants,  392. 

Saccharic  acid,  366. 
Saliva,  393. 
Salt,  428. 
Sand,  80. 
Sands,  73,  86. 

crops  for,  92. 

particles  of,  83. 
Sandstone,  73. 
Saponification,  351. 

value,  353. 

Secondary  minerals,  149,  151. 
Sedentary  soils,  61. 
Seeds,  ash  of,  21. 

classes,   379. 

need  oxygen,  43. 
Serpentine,  153. 


INDEX 


491 


Siderite,  154. 
Silage,  348,  385- 
Silica,    152. 

function  in  plants,  16. 
Silicates,  hydrated,  149,   152. 
Silt,  80. 

Soda,  not  essential,  16. 
Soil,  adhesion  in,  115. 
Soil  acidity,  160,  250,  253. 

air   space,   115. 
Soils,  alluvial  56,  66,  76. 
Soil  analysis,  167. 

apparent  specific,  gravity,  113. 

by  strong  acids,  161. 

interpretation,  173,  195. 
Soil  atmosphere,  51. 

arid,  178. 

Soil  bacteria,  204,  206. 
Soil  carbon  dioxide  of,  51- 

carbonate  of  lime  in  154,  186. 

chloroform  extract  of,  157. 

chemical  composition,  167. 

relation    to    adaptation    to    crops, 
II. 

classification,  85,  95,   117. 

cohesion,  115. 

color,  112. 

complete  analysis,   168. 

colluvial,  63. 

constituents,    149. 

crumbs,  90. 

cumulose,  63. 

deficiencies,    174,  244,  245. 

depth,    102. 

depth  limitations  of,  ic6. 

effects  of  manure  on,  290. 

ether  extract  of,   157. 

extract,  composition,  182. 

fertility  of,   relation  to  composi- 
tion,  171. 

relation  to  water,  123. 
Soil,  fixation  in,  234,  239. 

from  igneous  rocks,  63. 


Soil,  from  rocks,  54. 
glacial,  57,  68,   76,  97. 
investigation  of  minerals  of,  155. 
limestone,  73,   76,  90,  97. 
maps,  99. 
losses  and  gains   of,   61,   76,   271, 

341. 

mechanical  composition,  86. 
mechanical  analysis,  79. 
minerals,  147. 
minerals,  solubility,  183. 
muck,   74. 
organic  matter,   156,  228. 

ammonia-soluble,   162. 
particles,  relation  to  texture,  83. 
particles,  79. 
peat,  74. 

pentosans  in,  157. 
physical  properties,  101. 
provinces  of  the  U.  S.,  74- 
quantity  of  water  in,  127. 
retention  of  water  by,  134. 
sedentary,  61. 
series,  94. 
shrinking   of,    117. 
specific  gravity,    113. 
survey,  99. 
solutions,  199. 
temperature,   107,  no,   in. 
texture  and  composition  87. 
toxic  theory  of,  158. 
transported,  61. 
types,  94- 

types,  composition,  179. 
ventilation,   51. 
water,   132,    136,   138. 
water  control,  147. 
water  losses,   142. 
water  gains,  139. 
water  and  transpiration,   121. 
weathering,  61. 
water  in,  132. 
water-soluble  part,  196. 


492 


INDEX 


Soil,  water  extract,  201. 

water,  effect  on  temperature,  in. 

weight  per  foot,  114. 

wet   soils,   148. 

wind  blown,  71. 
Specific  gravity  of  soils,  113. 

Stachyose,  370. 

Stage   of   growth,    effect   on    diges- 
tion, 417. 
Starch,   367,   370. 

digestibility,  408. 

forms  fat,  441. 

loss  of  energy  of,  418. 

manufacture,  372. 

maintenance  value,  439. 

productive  value,  423. 
Steapsin,  394. 
Stilbite,  152. 
Stony  rock,  64. 
Straw,   22. 

Steers,    maintenance    ration,    439. 
Sheep,  composition  of  gain,  442. 

digestive  power,  402. 

fattening  ration,  449. 

maintenance  ration,  439. 
Subsoil,  101. 
Sucrose,   368. 
Sugar,  loss  in  drying,  347. 

productive   value,   422. 
Sugars,  361. 

digestibility,  408. 

fermentation,  364. 

manufacture,  368. 

value   for  maintenance,  436. 
Sulphate  of  ammonia,  294. 
Sulphate  of  potash,  370. 
Sulphur  dioxide  in  air,  49. 
Sulphur,  essential  to  plants,  18. 

in  soils,  258. 
Superphosphates,  307. 
Swamp,  139. 
Syenite,  65. 
Syrup,   369. 


Talc,   153. 

Tankage,   297. 

Tannic  acid,  376. 

Tartaric  acid,  376. 

Temperature,  weathering  by,  55. 

Therm,  377. 

Thermal  energy,  420,  427. 

'Thomas  phosphate,  306. 

Till,  69. 

Tilth,  90. 

Tobacco  grown  under  shade,  41. 

stems,  308. 

soils,  93- 

Tomatoes,  fertilizer  for,  345. 
Toxic  theory,  158. 
Transpiration,    119,   198. 
Transported  soils,   161. 
Tripsin,  394. 

Truck  crops,  fertilizer  for,  345. 
Tubercles,  12. 
Tyrosin,  359. 

Urea,  418. 
Uric  acid,  418. 
Urine,  418. 

Vivianite,   155. 

Valuation  of  fertilizers,  314. 

Water,  available,  136. 
Water,  control  of,  146. 

composition  of  rain,  49. 

evaporation,    145. 

estimation  in  plants,  347. 

effect    of    water    temperature    on 
food  required,  438. 

flowing  in  soils,  131. 

irrigation,   261. 
Water,  in  feeding,  431. 

in  plants,  346. 

losses  from  soil,  142. 

nitrogen  in  rain,  48. 

quality,  269. 

quantity   required  by  plants,    123. 
Water   culture,    10. 


INDEX 


493 


Water  capacity  of  soils,  201. 
Water-soluble,  soil  constituents,  196. 
Water  table,  107,  138. 
Wavellite,  155. 
Wax  alcohols,  355. 

digestion  of,  409. 
Weathering  agencies,  53. 

loss  by,  60. 

products   of,   59. 


Wheat  bran,  digestibility,  408. 
Wilting  coefficient,  137. 
Wire  basket  experiments,  249. 
Wood  ashes,  309. 
Work  animals,  feeding,  453. 

Xylose,  366. 
Yeast,  364. 
Zeolites,  152. 


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